bluebird

Timeouts

Timeouts in Bluebird Promises

What is a Timeout?

A timeout is a function that waits for a certain amount of time and then executes a callback if the wait completes without interruption. In Bluebird, timeouts are implemented using the Promise.timeout() function.

Creating a Timeout Promise

To create a timeout promise, you use the Promise.timeout(ms, value) syntax, where ms is the number of milliseconds to wait and value is the value to resolve with when the timeout finishes.

// Wait for 1 second and resolve with "Hello"
const timeoutPromise = Promise.timeout(1000, "Hello");

Executing a Timeout Promise

You can execute a timeout promise like any other promise. For example, to log the resolved value:

timeoutPromise.then(value => {
  console.log(value); // Output: "Hello"
});

Example Usage

Polling for a Response

Suppose you want to poll a server every 5 seconds until you receive a response. You can use a timeout promise to do this:

// Poll every 5 seconds until the server responds
function pollForResponse() {
  return fetch("https://example.com/api")
    .then(response => {
      if (response.ok) {
        return response.json();
      } else {
        // Server didn't respond, try again in 5 seconds
        return Promise.timeout(5000).then(pollForResponse);
      }
    });
}

pollForResponse().then(data => {
  // Server responded successfully, do something with the data
});

Setting Timeouts on Promises

You can also set a timeout on an existing promise using the Promise.timeout(ms, promise) syntax. If the promise takes longer than ms milliseconds to resolve, it will reject with a TimeoutError.

// Set a 5-second timeout on a promise
const promiseWithTimeout = Promise.timeout(5000, fetch("https://example.com/api"));

promiseWithTimeout.then(response => {
  // Request completed within 5 seconds
}).catch(error => {
  if (error instanceof TimeoutError) {
    // Request timed out
  }
});

Applications in the Real World

  • Server-side polling: Poll a server for updates at regular intervals.

  • Rate limiting: Limit the number of requests per second by setting a timeout on each request.

  • Error handling: Automatically retry failed operations after a timeout.

Promise.try()

Promise.try()

What is Promise.try()?

  • A convenience function that creates a new promise that resolves to the result of calling a function.

Syntax:

Promise.try(function)

Parameters:

  • function: A function that returns a value or a promise.

Returns:

  • A promise that resolves to the result of the function.

How it works:

  1. Promise.try() calls the provided function.

  2. If the function returns a value (e.g., a string, number, object), the promise is resolved with that value.

  3. If the function returns a promise, the returned promise is directly attached to the newly created promise. That means if the returned promise fulfills with a value, the attached promise also fulfills with the same value. Similarly, if the returned promise rejects with a reason, the attached promise also rejects with the same reason.

Real-World Example:

Consider a function that calculates the square root of a number:

function sqrt(num) {
  if (num < 0) {
    throw new Error("Cannot calculate square root of negative numbers");
  }
  return Math.sqrt(num);
}

We can use Promise.try() to convert this function into a promise:

const promise = Promise.try(sqrt, 9);
promise.then((result) => {
  console.log("Square root:", result); // 3
}).catch((error) => {
  console.log("Error:", error.message); // "Cannot calculate square root of negative numbers" if num is negative
});

Potential Applications:

  • Converting synchronous functions to asynchronous functions.

  • Handling asynchronous operations (e.g., reading files, making network requests) in a clean and concise way.

  • Chaining promises together to create complex asynchronous workflows.

Promise.some()

Promise.some()

Simplified Explanation:

Promise.some() allows you to wait for some, but not all, of a set of promises to resolve. Imagine you have a bag of marbles, and you want to wait until you find 3 red ones. You don't need to check every marble, just enough to find 3 red ones.

Syntax:

Promise.some(promises, count)

  • promises: An array of promises you want to check.

  • count: The number of promises that need to resolve.

Return Value:

Returns a Promise that resolves with an array of the resolved values of the first count promises.

Detailed Explanation:

Promise.some() starts by checking if the count is greater than the number of promises. If it is, it immediately rejects with an error.

Next, it creates a new array of promises that will be resolved. It then loops through the input array of promises and checks if each one resolves or rejects. If a promise resolves, it adds the resolved value to the array of resolved promises. If a promise rejects, it stops checking and immediately rejects the Promise.some() promise.

Once all the required promises have resolved, the Promise.some() promise resolves with the array of resolved values.

Code Examples:

// Find the first 3 fulfilled promises in the array
Promise.some([
  Promise.resolve(1),
  Promise.reject(2),
  Promise.resolve(3),
  Promise.resolve(4),
  Promise.resolve(5)
], 3).then((result) => {
  console.log(result); // [1, 3, 4]
}).catch((error) => {
  console.log(error); // Error: Promise rejected by a value that is not a Promise
});

Real-World Applications:

  • Parallel Processing: Checking for multiple data sources to be available before continuing.

  • Validation: Verifying the validity of multiple inputs before submitting a form.

  • Monitoring: Checking the status of multiple systems before alerting an operator.

Memory Management

Memory Management

Memory management refers to how a program stores and retrieves data in memory. In JavaScript, this is handled by the V8 engine, which uses a garbage collector to automatically manage memory allocation and deallocation.

Garbage Collector

The garbage collector is responsible for identifying and reclaiming memory that is no longer being used. It does this by tracking references to objects and freeing up memory when there are no more references pointing to them.

Memory Leak

A memory leak occurs when a program holds on to memory that is no longer needed, even though it is no longer being used. This can lead to performance issues and system crashes.

Weak References

Weak references are a way to store objects that do not prevent them from being garbage collected. This can be useful for caching objects that may not be used again, but that you want to keep around for a short period of time.

Promise Caching

Promise caching is a technique used to avoid re-running expensive asynchronous operations by storing the results in memory. This can be used to improve performance and reduce latency.

Real-World Applications

  • Caching: Storing data in memory to avoid fetching it from a slower source, such as a database or remote API.

  • Object Pooling: Reusing objects that are no longer needed, instead of creating new ones each time.

  • Garbage Collection Tuning: Adjusting the garbage collector's behavior to improve performance for specific applications.

Example:

// Caching
const cache = {};
async function fetchUser(id) {
  if (cache[id]) {
    return cache[id];
  }
  const user = await database.getUser(id);
  cache[id] = user;
  return user;
}

// Object Pooling
class ConnectionPool {
  constructor(maxConnections) {
    this.connections = [];
    this.maxConnections = maxConnections;
  }
  async getConnection() {
    if (this.connections.length > 0) {
      return this.connections.pop();
    }
    if (this.connections.length < this.maxConnections) {
      const connection = await createConnection();
      this.connections.push(connection);
      return connection;
    }
    return await Promise.race([
      getConnection(), // Wait for a connection to become available
      createConnection(), // Create a new connection if necessary
    ]);
  }
  releaseConnection(connection) {
    this.connections.push(connection);
  }
}

Promise.each()

Promise.each()

Purpose: Executes a series of asynchronous tasks in sequence, one at a time, and waits for each task to complete before moving on to the next.

Simplified Explanation:

Imagine you have a list of tasks that need to be done, like washing dishes, doing laundry, and mopping the floor. Promise.each() is like a helper that washes one dish, then dries it, then washes the next dish, and so on, until all the dishes are washed.

Code Snippet:

const tasks = ['wash dishes', 'do laundry', 'mop floor'];

Promise.each(tasks, (task) => {
  return doAsyncTask(task); // Function that performs the asynchronous task
})
.then(() => {
  // All tasks are complete
})
.catch((err) => {
  // An error occurred during one of the tasks
});

Real-World Applications:

  • Processing a large batch of data in sequence.

  • Fetching multiple resources from a server.

  • Running a series of tests or validations.

Advantages:

  • Ensures that tasks are executed in the specified order.

  • Handles errors gracefully by catching them for each task.

  • Makes it easy to process large batches of tasks without having to manage the flow manually.

Promise API Reference

1. Promise

  • Concept: A placeholder for a future value that may or may not be available yet.

  • Explanation: Like a promise you make to your friend to give them a gift later. You don't have the gift right now, but you promise to hand it over in the future.

2. then()

  • Purpose: Register a callback to be executed when the promise is fulfilled (gets a value).

  • Explanation: Like asking your friend when they'll be available to receive the gift you promised.

3. catch()

  • Purpose: Register a callback to be executed when the promise is rejected (fails to get a value).

  • Explanation: Like having a backup plan in case the gift shop runs out of the gift you wanted to give.

4. finally()

  • Purpose: Register a callback to be executed regardless of whether the promise is fulfilled or rejected.

  • Explanation: Like adding a note to the gift saying "I tried my best" even if you couldn't get the specific gift you promised.

5. resolve()

  • Purpose: Used internally to mark a promise as fulfilled and provide a value.

  • Explanation: Like handing over the gift to your friend.

6. reject()

  • Purpose: Used internally to mark a promise as rejected and provide a reason for failure.

  • Explanation: Like informing your friend that the gift is unavailable.

Real-World Examples:

Example 1: Fetching data from an API:

// Use a promise to fetch data from an API
fetch('https://example.com/api/data')
  // Register a callback for when the promise is fulfilled
  .then(response => response.json())
  // Register a callback for when the promise is rejected
  .catch(error => console.error(error));

Example 2: Checking for user input:

// Use a promise to check for user input
const inputPromise = new Promise((resolve, reject) => {
  // Resolve the promise when the user enters input
  document.addEventListener('input', e => resolve(e.target.value));
  // Reject the promise if the user cancels or closes the input form
  document.addEventListener('cancel', () => reject('User canceled input'));
});

// Register a callback for when the promise is fulfilled
inputPromise.then(value => console.log(value));
// Register a callback for when the promise is rejected
inputPromise.catch(error => console.error(error));

Error Handling

Error Handling in Node.js with Bluebird

Promises & Bluebird

  • Promises are objects that represent the outcome of an asynchronous operation.

  • Bluebird is a popular library that enhances the functionality of Promises in Node.js.

Error handling with Promises

  • Promises can either be resolved (successful) or rejected (unsuccessful).

  • Errors in Promises are handled using the .catch() method, which takes a function that will be called if the Promise is rejected.

Simplified Example:

// A simple Promise that resolves
const myPromise = Promise.resolve('Success!');

// Handle the resolution (if successful)
myPromise.then(result => console.log(result)); // Logs 'Success!'

// A simple Promise that rejects
const myErrorPromise = Promise.reject('Error!');

// Handle the rejection (if unsuccessful)
myErrorPromise.catch(error => console.log(error)); // Logs 'Error!'

Error Handling with Bluebird

  • Bluebird provides enhanced error handling capabilities.

  • It allows you to:

    • Customize error messages

    • Define custom error classes

    • Handle multiple errors (e.g., using Promise.allSettled)

Simplified Example using Bluebird:

// Import Bluebird
const { Promise } = require('bluebird');

// Error class with a customized message
class MyError extends Error {
  constructor(message) {
    super(message);
    this.name = 'MyError';
  }
}

// Create a Promise that rejects with MyError
const myErrorPromise = Promise.reject(new MyError('My custom error!'));

// Handle the rejection with a specific error class
myErrorPromise.catch(MyError, error => console.log(error.message)); // Logs 'My custom error!'

Real-World Application:

  • HTTP Request Handling: Error handling is crucial for handling failures in HTTP requests (e.g., server errors, network issues).

  • Data Validation: Promises and error handling can be used to validate user input and handle errors gracefully.

  • Concurrency: Bluebird's enhanced error handling capabilities are particularly useful in handling errors in concurrent operations (e.g., Promise.allSettled).

Performance Considerations

Performance Considerations

1. Use Promises, not Callbacks:

  • Why: Promises chain asynchronously, allowing multiple operations to execute concurrently. Callbacks execute sequentially, blocking subsequent operations.

  • Code Example:

// Using callbacks (sequential)
api.get("user1", (err, user1) => {
  if (err) return console.log(err);
  api.get("user2", (err, user2) => {
    if (err) return console.log(err);
    console.log([user1, user2]);
  });
});

// Using promises (concurrent)
api.get("user1").then(user1 => {
  return api.get("user2").then(user2 => {
    console.log([user1, user2]);
  });
});

2. Avoid Nested Promises:

  • Why: Nested promises can create a "callback hell" scenario, making code difficult to maintain.

  • Code Example:

// Nested promises
api.get("user1").then(user1 => {
  return api.get("user2").then(user2 => {
    return api.get("user3").then(user3 => {
      console.log([user1, user2, user3]);
    });
  });
});

// Flattened promises using Promise.all
Promise.all([api.get("user1"), api.get("user2"), api.get("user3")]).then(users => {
  console.log(users);
});

3. Use Parallelization:

  • Why: Parallelization allows multiple asynchronous operations to execute simultaneously, improving performance.

  • Code Example:

// Using Promise.map
Promise.map([1, 2, 3], async (num) => {
  // Do something with each number
  return num * 2;
}).then(results => {
  console.log(results); // [2, 4, 6]
});

4. Consider Concurrency Limits:

  • Why: Excessive concurrency can overwhelm the system and slow down performance.

  • Code Example:

// Using a concurrency limit with Promise.map
Promise.map([1, 2, 3], async (num) => {
  // Do something with each number
  return num * 2;
}, {concurrency: 2}).then(results => {
  console.log(results); // [2, 4, 6]
});

5. Take Advantage of Optimization Features:

  • Why: Bluebird offers various optimization features to improve performance, such as Just-In-Time (JIT) compilation and optimized data structures.

  • Code Example: (JIT compilation is enabled by default)

// Using JIT compilation
Promise.defer().resolve(42).then(value => {
  console.log(value); // 42
});

6. Monitor and Profile Performance:

  • Why: Monitoring and profiling performance helps identify bottlenecks and optimize code.

  • Code Example:

// Using performance.now() to measure execution time
const start = performance.now();
api.get("user1").then(user1 => {
  api.get("user2").then(user2 => {
    console.log([user1, user2]);
    const end = performance.now();
    console.log(`Execution time: ${(end - start).toFixed(2)} ms`);
  });
});

Real World Applications:

  • Concurrent Fetching of Data: Use parallelization and promises to concurrently fetch data from multiple sources, such as fetching user details and product information.

  • Concurrency Control: Limit concurrency to avoid overloading the server or causing performance issues.

  • Performance Optimization: Use Bluebird's optimization features and monitor performance to identify and resolve bottlenecks in complex asynchronous code.

Cancellation

Cancellation

In Node.js Bluebird, cancellation allows you to stop an asynchronous operation that is in progress. This can be useful in various situations, such as when a user cancels a request or when a particular operation is no longer needed.

How it works:

Bluebird provides a CancellationToken class that represents a cancellable operation. To create a cancellation token, use the CancellationToken.create() method:

const cancelToken = CancellationToken.create();

Once you have a cancellation token, you can pass it to an asynchronous function that supports cancellation. For example, the following function takes a cancellation token and cancels the operation if the token is cancelled:

async function cancellableOperation(cancelToken) {
  try {
    // Perform some asynchronous work
    await Promise.delay(1000); // Simulate asynchronous work

    // Check if the token is cancelled
    if (cancelToken.isCancelled()) {
      // Operation was cancelled, throw an error
      throw new Error("Operation cancelled");
    }

    // Operation completed successfully
    return "Operation completed";
  } catch (err) {
    // Handle the error
    console.error(err);
  }
}

To cancel the operation, simply call the cancel() method on the cancellation token:

cancelToken.cancel();

This will cause the asynchronous function to throw an error indicating that the operation was cancelled.

Real-world applications:

Cancellation can be used in various real-world applications, such as:

  • User cancellation: Allowing users to cancel long-running or unnecessary operations.

  • Data synchronization: Ensuring that data is synchronized only when it is needed.

  • Resource management: Releasing resources when operations are cancelled.

Complete code implementation:

Here is a complete code implementation that demonstrates the use of cancellation in Bluebird:

const { CancellationToken } = require("bluebird");

const cancelToken = CancellationToken.create();

async function cancellableOperation(cancelToken) {
  try {
    // Perform some asynchronous work
    await Promise.delay(1000); // Simulate asynchronous work

    // Check if the token is cancelled
    if (cancelToken.isCancelled()) {
      // Operation was cancelled, throw an error
      throw new Error("Operation cancelled");
    }

    // Operation completed successfully
    return "Operation completed";
  } catch (err) {
    // Handle the error
    console.error(err);
  }
}

// Start the cancellable operation
cancellableOperation(cancelToken).then((result) => {
  console.log(result);
});

// After 500ms, cancel the operation
setTimeout(() => {
  cancelToken.cancel();
}, 500);

Generators and Coroutines

Generators

Simplified Explanation: Generators are functions that can be paused and resumed without losing their state. This allows you to create functions that can yield multiple values over time.

Code Snippet:

function* myGenerator() {
  yield 1;
  yield 2;
  yield 3;
}

Real-World Example: Generators can be used to represent iterators, such as a list of numbers or words. You can iterate over the generator's values one at a time using a for...of loop.

Potential Applications:

  • Creating iterators for lazy evaluation of data structures

  • Generating sequences of values based on certain criteria

Coroutines

Simplified Explanation: Coroutines are like generators, except that they can be paused and resumed in multiple threads of execution. This allows for more complex interactions between concurrent tasks.

Code Snippet:

async function myCoroutine() {
  const value = await Promise.resolve(1);
  yield value;
  const anotherValue = await Promise.resolve(2);
  yield anotherValue;
}

Real-World Example: Coroutines can be used to implement concurrent processes within a single thread. This allows you to write code that looks and feels like it's running in parallel, but without the overhead of true multithreading.

Potential Applications:

  • Managing asynchronous operations

  • Implementing cooperative multitasking

  • Writing web servers using event-driven programming

Code Implementation and Example

Generator implementation:

// Generator to generate Fibonacci numbers
function* fibonacci() {
  let a = 0;
  let b = 1;

  while(true) {
    yield a;
    [a, b] = [b, a + b];
  }
}

// Iterate over the generator and print the first 10 Fibonacci numbers
for (const number of fibonacci()) {
  console.log(number);
  if (number > 100) { break; }
}

Coroutine implementation:

// Coroutine to calculate the factorial of a number
async function factorial(n) {
  if (n <= 1) {
    return 1;
  }

  return n * await factorial(n - 1);
}

// Start the coroutine and wait for the result
factorial(5).then((result) => { console.log(result); });

Promise.race()

Promise.race()

Simplified Explanation:

Imagine a race between multiple promises. The first promise to "finish" (i.e., resolve or reject) wins the race, and the result is returned.

Detailed Explanation:

  • Syntax: Promise.race(iterable)

    • iterable is an array or iterable object containing multiple promises.

  • Returns: A new Promise that resolves or rejects when the first promise in the iterable settles.

  • Behavior:

    • If the first promise resolves, the returned Promise will resolve with the same value.

    • If the first promise rejects, the returned Promise will reject with the same error.

    • If multiple promises settle at the same time, the returned Promise prefers the first one it receives.

Code Snippet:

const promise1 = new Promise((resolve, reject) => setTimeout(resolve, 1000));
const promise2 = new Promise((resolve, reject) => setTimeout(resolve, 500));
const promise3 = new Promise((resolve, reject) => setTimeout(resolve, 1500));

Promise.race([promise1, promise2, promise3])
  .then((result) => {
    // Result would be the value of either promise1 or promise2 (whichever resolves first)
  })
  .catch((error) => {
    // Error would be the error of either promise1 or promise2 (whichever rejects first)
  });

Real-World Applications:

  • Loading multiple assets in parallel: Race promises to load images, scripts, or other assets, and use the first one to finish to display or use.

  • Polling for data: Race multiple HTTP requests to fetch data from different sources, and use the first response to avoid unnecessary delays.

  • Timeout handling: Specify a timeout and race it against a long-running operation. If the timeout occurs, reject the returned Promise.

Potential Applications:

  • Website optimization by loading assets faster

  • Improved user experience by reducing data retrieval time

  • Error handling and recovery scenarios

Debugging

Debugging Bluebird Promises

1. Using debugger;

Add debugger; statements to your code to pause execution and inspect variables in the debugger.

Example:

Bluebird.resolve(10)
  .then(() => {
    debugger; // Pause execution here
  });

2. Using the .tap() Method

tap allows you to execute a side effect (e.g., logging) without changing the promise result.

Example:

Bluebird.resolve(10)
  .tap(val => console.log('Value:', val));

3. Using .catch()

.catch() handles rejected promises and allows you to log errors or handle them gracefully.

Example:

Bluebird.resolve(10)
  .then(() => Promise.reject(new Error('Oops')))
  .catch(err => console.error(err));

4. Using .finally()

.finally() executes a callback regardless of whether the promise resolves or rejects. It's useful for cleanup tasks or logging.

Example:

Bluebird.resolve(10)
  .then(() => console.log('Resolved'))
  .catch(err => console.error(err))
  .finally(() => console.log('Finally executed'));

5. Using the inspect() Method

inspect() returns a human-readable representation of a promise's state, making it easier to debug.

Example:

const myPromise = Bluebird.resolve(10);
console.log(myPromise.inspect());

Applications:

  • Error handling: Debugging rejections and logging error messages.

  • Logging progress: Using tap to log intermediate results.

  • Cleanup tasks: Using finally to ensure tasks are executed regardless of outcome.

  • Debugging promise chains: Using debugger to pause execution and examine promise states.

  • Inspecting promise state: Using inspect to understand promise resolution/rejection status.

Promisification

Promisification

Promisification is a pattern for converting callbacks to Promises. It allows you to make asynchronous code more manageable and readable.

How it works:

  • Callback functions: Functions that take a callback function as an argument to be called when the task is complete.

  • Promises: Objects that represent future values that may or may not be available yet.

Steps to promisify a function:

  1. Wrap the function in a Promise: Return a new Promise from the function.

  2. Resolve the Promise: When the callback is called successfully, resolve the Promise with the result.

  3. Reject the Promise: When the callback fails, reject the Promise with the error.

Example:

Let's say we have a function that reads a file asynchronously:

const readFile = (filename, callback) => {
  fs.readFile(filename, (err, data) => {
    callback(err, data);
  });
};

To promisify this function, we would do the following:

const readFilePromisified = (filename) => {
  return new Promise((resolve, reject) => {
    readFile(filename, (err, data) => {
      if (err) {
        reject(err);
      } else {
        resolve(data);
      }
    });
  });
};

Now we can use readFilePromisified like this:

readFilePromisified('file.txt')
  .then((data) => {
    // Do something with the data
  })
  .catch((err) => {
    // Handle the error
  });

Real-world applications:

Promisification is useful in any situation where you want to make asynchronous code easier to manage:

  • Improving code readability: Promises make it clear when an operation is asynchronous, improving code readability.

  • Chaining operations: Promises allow you to chain multiple asynchronous operations together, making it easy to create complex workflows.

  • Error handling: Promises provide a clean way to handle errors, simplifying error handling in asynchronous code.

Promise.all()

Promise.all()

What is Promise.all()?

Promise.all() is a function that takes an array of promises and returns a single promise that resolves when all of the input promises have resolved. The returned promise's value is an array containing the values of the input promises in the same order.

Simplified Explanation:

Imagine you have a list of tasks that you need to complete, and each task is represented by a promise. Promise.all() allows you to wait for all of these tasks to finish and then get the results of all of them in one go.

Code Snippet:

const promises = [
  Promise.resolve(1),
  Promise.resolve(2),
  Promise.resolve(3)
];

Promise.all(promises).then((results) => {
  // results will be [1, 2, 3]
});

Real World Example:

Consider an e-commerce website where you need to fetch product details from multiple APIs. Instead of waiting for each API call to return, you can use Promise.all() to fetch all the product details in one go.

Implementation:

const getProductDetails = (id) => {
  return Promise.resolve(`Product ${id} details`);
};

const ids = [1, 2, 3];

Promise.all(ids.map(getProductDetails)).then((results) => {
  // results will be ["Product 1 details", "Product 2 details", "Product 3 details"]
});

Applications:

  • Concurrently fetching data from multiple sources

  • Validating multiple form fields before submitting

  • Loading multiple assets (e.g., images, scripts) before rendering a page

Promise.join()

Promise.join()

Simplified Explanation:

Promise.join() is a function that takes multiple Promises as arguments and returns a single Promise that resolves to an array of the resolved values of the input Promises.

Detailed Explanation:

  • Input: Takes multiple Promises as arguments.

  • Execution: Executes all the input Promises concurrently.

  • Result: Returns a single Promise that resolves to an array of the resolved values of the input Promises.

  • Order: The order of the values in the result array corresponds to the order of the input Promises.

Code Snippet:

Promise.join(promise1, promise2, promise3)
  .then((result) => {
    // result is an array of the resolved values of promise1, promise2, and promise3
  })
  .catch((error) => {
    // Handle the error if any of the promises reject
  });

Real-World Applications:

  • Concurrently load data from multiple sources and then combine it.

  • Execute a sequence of tasks that depend on each other.

  • Wait for multiple events to occur before proceeding.

Example:

// Load user data and their recent activity concurrently
const userDataPromise = getUserData();
const activityDataPromise = getUserActivity();

Promise.join(userDataPromise, activityDataPromise)
  .then((result) => {
    // result[0] contains the user data, result[1] contains the activity data
    // Combine the data and display it
  });

Installation and Setup

Installation and Setup

Installing Bluebird

To install Bluebird, run the following command:

npm install --save bluebird

Using Bluebird

Once installed, you can use Bluebird by requiring it in your Node.js script:

const Promise = require('bluebird');

Creating Promises

Bluebird promises can be created using the Promise.resolve() and Promise.reject() functions:

const promise1 = Promise.resolve('Hello, world!');
const promise2 = Promise.reject(new Error('Something went wrong'));

Consuming Promises

Promises can be consumed using the then() and catch() methods:

promise1.then(data => {
  console.log(data); // 'Hello, world!'
});

promise2.catch(error => {
  console.error(error); // Error: Something went wrong
});

Chaining Promises

Promises can be chained together using the then() method:

promise1.then(data => {
  return Promise.resolve(data + '!');
}).then(data => {
  console.log(data); // 'Hello, world!'
});

Handling Errors

Errors can be handled using the catch() method:

promise1.then(data => {
  return Promise.reject(new Error('Something went wrong'));
}).catch(error => {
  console.error(error); // Error: Something went wrong
});

Real-World Applications

Bluebird is used in a wide variety of applications, including:

  • Web development

  • Data processing

  • Machine learning

  • Testing

Potential Applications

Here are a few potential applications for Bluebird:

  • Using Bluebird to handle asynchronous operations in a Node.js web server

  • Using Bluebird to process large datasets in parallel

  • Using Bluebird to train machine learning models

  • Using Bluebird to write unit tests for Node.js applications

Promise.reject()

Promise.reject()

A Promise is an object that represents the eventual completion or failure of an asynchronous operation. The Promise.reject() method is used to reject a Promise, which means that the operation failed.

How it works:

When you call Promise.reject(), you pass it a value that represents the reason why the Promise failed. This value can be anything (e.g., an error object, a string, or a number).

Once the Promise is rejected, it will never resolve. This means that any code that is waiting for the Promise to resolve will never be executed.

Example:

const promise = new Promise((resolve, reject) => {
  // Try to do something asynchronous
  try {
    // Do something that might fail
  } catch (error) {
    // If it fails, reject the Promise with the error
    reject(error);
  }
});

promise.then((result) => {
  // This code will never be executed because the Promise was rejected
  console.log('Success!', result);
}).catch((error) => {
  // This code will be executed because the Promise was rejected
  console.log('Error!', error);
});

In this example, the Promise is rejected with an error object. The catch() method is called when the Promise is rejected, and it logs the error to the console.

Real-world applications:

Promise.reject() can be used in any situation where you need to handle the failure of an asynchronous operation. For example, you could use it to:

  • Handle errors in AJAX requests

  • Deal with failed file uploads

  • Notify other parts of your application when an operation has failed

Conclusion:

Promise.reject() is a powerful tool for handling errors in asynchronous operations. It allows you to reject a Promise with a value that represents the reason for the failure, and it prevents any code that is waiting for the Promise to resolve from being executed.

Promises Basics

Promises Basics

What is a Promise?

  • A promise is like a guarantee. It represents a value that will become available in the future.

  • You can use promises to handle asynchronous operations, such as fetching data from the internet or reading a file.

Creating a Promise

// Create a promise that will resolve with the value "Hello World!"
const promise = new Promise((resolve, reject) => {
  resolve("Hello World!");
});

Resolving a Promise

  • When the operation you're waiting for completes successfully, you call the resolve() function to resolve the promise with the result.

Rejecting a Promise

  • If the operation you're waiting for fails, you call the reject() function to reject the promise with an error.

Consuming a Promise

  • To consume a promise, you use the then() method.

  • The then() method takes two arguments:

    • A callback function that will be called when the promise resolves.

    • A callback function that will be called when the promise rejects.

Example:

// Consume the promise
promise.then((result) => {
  console.log(result); // "Hello World!"
}, (error) => {
  console.log(error); // Error message
});

Chaining Promises

  • You can chain promises to create a sequence of asynchronous operations.

  • Each promise in the chain depends on the previous promise resolving.

Example:

// Fetch a list of users
const users = fetchUsers();

// Then, for each user, fetch their profile
users.then((users) => {
  const promises = users.map((user) => fetchProfile(user));
  return Promise.all(promises);
});

// Finally, display the profiles
.then((profiles) => {
  displayProfiles(profiles);
});

Real-World Applications

  • Fetching data from the internet: You can use promises to handle asynchronous HTTP requests, such as fetching data from a remote API.

  • Reading files: You can use promises to handle asynchronous file I/O operations, such as reading a file from disk.

  • Performing background tasks: You can use promises to delegate tasks to a background thread, allowing the main thread to continue executing.

Rejection Events

Rejection Events

When a Promise is rejected, it triggers a "rejection event". This event allows you to handle the error and decide what to do next.

Handling Rejection Events

There are two ways to handle rejection events:

  • Using .catch(): Appends a callback function to the Promise. This function will be called when the Promise is rejected, and it can handle the error.

  • Using Promise.onUnhandledRejection(): Registers a global event handler for unhandled rejections. This handler will be called whenever a rejection event is not handled by a .catch() block.

Examples

Using .catch():

const promise = Promise.reject(new Error('Something went wrong'));

promise.catch(error => {
  // Handle the error here
  console.log(error.message); // Output: Something went wrong
});

Using Promise.onUnhandledRejection():

Promise.onUnhandledRejection(error => {
  // Handle the error here
  console.log(error.message); // Output: Something went wrong
});

// Create a rejected Promise and don't handle its rejection
const unhandledPromise = Promise.reject(new Error('Something went wrong'));

Real-World Applications

Rejection events are useful for:

  • Error handling and logging

  • Retrying failed operations

  • Displaying error messages to users

  • Preventing unhandled rejection errors from crashing your application

Resource Management

Resource Management in Bluebird Promises

Introduction:

Bluebird provides built-in features to help manage resources efficiently within promises. This is important because promises can hold onto resources indefinitely, which can lead to memory leaks and performance issues.

Topics:

1. Automatic Release:

  • When a promise resolves or rejects, any associated resources are automatically released.

  • This prevents memory leaks by ensuring that resources are not kept unnecessarily.

Example:

Promise.resolve('hello world').then(
  (result) => {
    // Resources associated with the promise are released here
  },
  (error) => {
    // Resources associated with the promise are released here
  }
);

2. Manual Release:

  • Sometimes, it's necessary to manually release resources before the promise resolves.

  • This can be done using the finally() method.

Example:

const fs = require('fs');

Promise.resolve().then(
  () => {
    return fs.readFile('file.txt');
  }
).finally(() => {
  // Manually release resources here, such as closing the file descriptor
  fs.close(fileDescriptor);
});

3. Disposable Resources:

  • Bluebird introduces the concept of "disposable resources".

  • These are objects that can be automatically released when a promise resolves or rejects.

  • They implement the dispose() method, which performs the cleanup.

Example:

const dbConnection = {
  dispose() {
    // Close the database connection
  }
};

Promise.resolve().then(() => {
  return dbConnection;
}).dispose();

4. Resource Management with Promises and Observables:

  • Bluebird provides extensions for observables that support resource management.

Example:

const Observable = require('rxjs/Observable');

const observable = Observable.create((observer) => {
  // Subscribe to the observable
  observer.next('Hello world!');
}).dispose();

Applications:

  • Memory management: Prevents memory leaks by automatically releasing resources.

  • Performance optimization: Improves performance by avoiding resource overuse.

  • Code clarity: Makes code more readable and easier to debug.

  • Resource isolation: Ensures that resources are released in a consistent manner, preventing interference between promises.

Best Practices

Best Practices for Writing Asynchronous Code with Bluebird

1. Use Promises Instead of Callbacks

  • What it means: Promises are a modern way to handle asynchronous operations. They're easier to read and write than callbacks, and they avoid the "callback hell" problem.

  • Simplified explanation: Imagine you're ordering food at a restaurant. With callbacks, you would give the waiter your order and he would tell you when it's ready. With promises, he would give you a note with a number on it. When your food is ready, you go to the counter and give them the number, and they'll give you your food.

  • Code snippet:

// Callback
fs.readFile('file.txt', function(err, data) {
  if (err) {
    console.error(err);
    return;
  }

  console.log(data.toString());
});

// Promise
fs.readFile('file.txt')
  .then(data => console.log(data.toString()))
  .catch(err => console.error(err));

2. Use Promise.all to Run Multiple Promises Concurrently

  • What it means: Promise.all allows you to run multiple promises at the same time, and wait for all of them to finish.

  • Simplified explanation: Imagine you want to download three files from the internet. You could use three separate readFile calls, and wait for each one to finish individually. With Promise.all, you can start downloading all three files at the same time, and then wait for all of them to finish before continuing.

  • Code snippet:

Promise.all([
  fs.readFile('file1.txt'),
  fs.readFile('file2.txt'),
  fs.readFile('file3.txt')
])
  .then(data => console.log(data))
  .catch(err => console.error(err));

3. Use Error Handling

  • What it means: Error handling is essential in asynchronous code. Bluebird supports two types of error handling: try/catch and unhandled rejection handling.

  • Simplified explanation: Imagine you're playing a game. With try/catch, you can catch errors that occur during the game and handle them gracefully. With unhandled rejection handling, you can define what should happen if an error occurs and is not caught by a try/catch block.

  • Code snippet:

try {
  await Promise.reject(new Error('Something went wrong!'));
} catch (err) {
  console.error(err);
}

4. Use finally to Execute Code Regardless of Promise Fulfillment

  • What it means: The finally block is executed regardless of whether the promise is fulfilled or rejected.

  • Simplified explanation: Imagine you're baking a cake. The finally block is like the cleanup step after you're done baking. You can use it to turn off the oven, wash the dishes, or do whatever else you need to do after the cake is finished.

  • Code snippet:

Promise.resolve('Hello world!')
  .then(data => console.log(data))
  .finally(() => console.log('Finished!'));

Real-World Applications

  • Web development: Asynchronous code is a must-have for building responsive and user-friendly web applications.

  • Data fetching: Promises and Promise.all can be used to fetch multiple data sources concurrently, improving performance and reducing latency.

  • Error handling: Robust error handling is crucial for ensuring that applications handle unexpected situations gracefully and avoid crashes.

  • Background tasks: finally can be used to clean up resources or perform additional tasks after a background task has completed.

Contributing to Bluebird

Contributing to Bluebird

Bluebird is an open-source JavaScript library that provides a set of utilities to handle asynchronous operations in a clean and consistent way. If you're interested in contributing to Bluebird, here's a simplified overview of the process:

1. Create a Fork

First, create a fork of the official Bluebird repository on GitHub. This will create a copy of the code in your own account.

2. Make Changes

Clone your fork to your local machine and make the necessary changes. If you're fixing a bug, add a test case that demonstrates the issue and verifies your fix.

3. Submit a Pull Request

Once you're satisfied with your changes, push them to your fork and create a pull request. This sends your changes to the maintainers of the official Bluebird repository for review.

4. Get Feedback

The maintainers will review your pull request and provide feedback. They may ask you to make further changes or provide additional information.

5. Iterate and Merge

Address any feedback and iterate on your changes until they are accepted. Once your pull request is merged, your changes will become part of the official Bluebird repository.

Real-World Example

Let's say you find a bug in Bluebird that prevents promises from resolving correctly in certain situations. To fix this bug, you would:

  1. Fork the Bluebird repository and make a copy on your local computer.

  2. Write a test case that reproduces the bug and demonstrates your fix.

  3. Create a pull request on GitHub, attaching your test case and describing your changes.

  4. The maintainers would review your pull request and provide feedback.

  5. You would iterate on your changes until they are accepted and merged into the official Bluebird repository.

Potential Applications

Contributing to Bluebird allows you to improve a widely used library that is essential for asynchronous programming in JavaScript. Your contributions can:

  • Fix bugs and improve the stability of the library.

  • Add new features and enhancements.

  • Help make the library more accessible and user-friendly.

Promise.resolve()

Promise.resolve()

What is it?

Promise.resolve() is a function that creates a new Promise and resolves it with a given value immediately.

How does it work?

When you call Promise.resolve(value), it creates a new Promise object and immediately sets its status to "resolved". The value you passed to the function becomes the value of the Promise.

Example:

const promise = Promise.resolve("Hello, world!");

promise.then(value => {
  console.log(value); // Logs "Hello, world!"
});

Applications:

  • Handling asynchronous operations where the result is already known.

  • Converting non-Promises to Promises for easier chaining.

  • Using as a placeholder for Promises in cases where the actual Promise is not yet available.

Real-World Example:

// Function to fetch data from a server
function fetchData() {
  return Promise.resolve({ name: "John Doe", age: 25 });
}

// Function to display data
function displayData(data) {
  console.log(data.name, data.age);
}

// Call the data fetching function and display the data
fetchData().then(displayData);

In this example, Promise.resolve() is used to create a Promise that immediately resolves with the data returned from the fetchData() function. This allows us to easily chain the displayData() function to display the data once it becomes available.

Promise.any()

Promise.any()

Simplified Explanation

Imagine you have multiple promises, and you want to know when any one of them resolves. Promise.any() helps you with that. It takes an array of promises and returns a new promise that resolves as soon as any of the input promises resolves.

Detailed Explanation

Promise.any() takes an array of promises as an argument and returns a new promise:

  • If any of the input promises resolves, the new promise resolves with the value of that promise.

  • If all the input promises reject, the new promise rejects with an aggregate error containing the errors from all the rejected promises.

Code Snippet

const promises = [
  Promise.resolve('Success 1'),
  Promise.reject('Error 1'),
  Promise.resolve('Success 2'),
];

Promise.any(promises)
  .then(result => {
    console.log('First resolved promise result:', result);
  })
  .catch(error => {
    console.log('All promises rejected:', error);
  });

Real-World Applications

  • Checking for server availability: You can use Promise.any() to check if any of multiple servers are available. The first server that responds will resolve the Promise.any().

  • Submitting multiple forms: If you have multiple forms on a page that are independent of each other, you can use Promise.any() to wait for the first form to be submitted and then proceed with the next step.

  • Loading external resources: If you need to load multiple external resources, such as images or scripts, you can use Promise.any() to load the first resource that becomes available.

Integration with Other Libraries

Integration with Other Libraries

Bluebird is a promise library that provides a robust and consistent interface to handle asynchronous tasks. It can be integrated with various other libraries to enhance its functionality.

Promises/A+ Compatibility

  • Bluebird follows the Promises/A+ specification, which defines a common interface for promises across different libraries.

  • This ensures that code written for Bluebird can easily be used with other compliant libraries.

Example:

// Define a promise using Bluebird
const promise = Promise.resolve(42);

// Use the promise with the Q library
const Q = require('q');
Q(promise).then((value) => {
  console.log(`Q resolved with: ${value}`);
});

Node.js EventEmitter

  • Bluebird can be integrated with Node.js EventEmitter to handle asynchronous events.

  • It provides a fromEvent method that converts an event emitter into a promise.

Example:

const fs = require('fs');

// Create a read stream
const readStream = fs.createReadStream('file.txt');

// Convert the stream into a promise
const streamPromise = Bluebird.fromEvent(readStream, 'data');

// Handle the promise
streamPromise.then((data) => {
  console.log(`Received data: ${data}`);
});

Node.js Streams

  • Bluebird can handle Node.js streams, such as read streams and write streams, using its promisifyAll method.

  • This simplifies asynchronous stream operations.

Example:

const fs = require('fs');

// Create a read stream
const readStream = fs.createReadStream('file.txt');

// Promisify all stream methods
Bluebird.promisifyAll(readStream);

// Read the stream asynchronously
readStream.readAsync().then((data) => {
  console.log(`Read data: ${data}`);
});

Real World Applications:

  • Promises/A+ Compatibility: Allows integration with other popular promise libraries, such as Q, es6-promise, and others.

  • Node.js EventEmitter: Facilitates handling asynchronous events in a consistent and reliable manner.

  • Node.js Streams: Simplifies asynchronous stream operations, making it easier to handle data streams.

Note: These are just a few examples of Bluebird's integration capabilities. It can also be integrated with other libraries, such as lodash, chai, and express, to enhance its functionality and applicability.

Promise Constructor

Promise Constructor

A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation. It's like a placeholder for the result of an action that hasn't happened yet.

When you create a Promise, you provide it with a function called an "executor". This function takes two arguments, resolve and reject. Inside the executor, you perform the asynchronous operation, and when it finishes, you call resolve if it succeeded or reject if it failed.

Here's an example of creating a Promise:

const promise = new Promise((resolve, reject) => {
  // Perform asynchronous operation here
  if (operation succeeded) {
    resolve(result);
  } else {
    reject(error);
  }
});

Executor Function

The executor function is a callback function that you provide when creating a Promise. It takes two arguments, resolve and reject.

The resolve function is called when the asynchronous operation succeeds. It takes one argument, which is the result of the operation.

The reject function is called when the asynchronous operation fails. It takes one argument, which is the error associated with the failure.

Consuming Promises

Once you have created a Promise, you can consume it using .then() and .catch() methods.

The .then() method takes two callback functions, onFulfilled and onRejected. onFulfilled is called when the Promise resolves, and onRejected is called when the Promise rejects.

The .catch() method is similar to .then(), but it only takes one callback function, onRejected. It's called when the Promise rejects.

Here's an example of consuming a Promise:

promise.then(onFulfilled, onRejected);

Real-World Applications

Promises are used in a wide variety of applications, including:

  • Handling asynchronous operations in web applications

  • Performing multiple asynchronous operations in parallel

  • Implementing retry logic for failed operations

  • Handling errors in complex systems

Code Implementations and Examples

Here's an example of a complete code implementation using Promises:

const promise = new Promise((resolve, reject) => {
  // Perform asynchronous operation here
  if (operation succeeded) {
    resolve(result);
  } else {
    reject(error);
  }
});

promise.then(
  (result) => {
    // Operation succeeded
  },
  (error) => {
    // Operation failed
  }
);

Bluebird Release Notes

1. Non-Error Throwables

Simplified Explanation:

Imagine you're coding a car, and instead of throwing an Error when a tire goes flat, you throw a "FlatTire" object. This allows you to handle the flat tire more specifically than just a generic Error.

Real-World Implementation:

// Create a custom Error subclass
class FlatTireError extends Error {
  constructor() {
    super('Flat tire!');
  }
}

// Throw the custom error
try {
  driveCar();
} catch (err) {
  if (err instanceof FlatTireError) {
    console.log('Oh no, a flat tire!');
  } else {
    console.log('Some other error occurred.');
  }
}

Potential Application:

This allows for more precise error handling in situations where different types of errors require different responses.

2. Promise.prototype.finally

Simplified Explanation:

This method allows you to run some code no matter what, whether a promise resolves or rejects. It's like a "cleanup" function that always runs.

Real-World Implementation:

// Perform an action and handle any errors
Promise.resolve()
  .then(() => {
    // Success handler
  })
  .catch((err) => {
    // Error handler
  })
  .finally(() => {
    // Cleanup code
  });

Potential Application:

This is useful for releasing resources, closing connections, or performing any cleanup that needs to happen regardless of the promise's outcome.

3. Promise.prototype.timeout

Simplified Explanation:

This method allows you to set a timeout for a promise. If the promise doesn't resolve within the specified time, it will throw a TimeoutError.

Real-World Implementation:

// Perform an action and wait up to 5 seconds for a response
const promise = Promise.resolve();
promise.timeout(5000);

// Handle the timeout
promise.catch((err) => {
  if (err instanceof TimeoutError) {
    console.log('No response received within 5 seconds.');
  }
});

Potential Application:

This is useful for ensuring that operations don't hang indefinitely and handling timeouts gracefully.

4. Promise.race

Simplified Explanation:

This method returns a promise that resolves or rejects as soon as the first promise in the array resolves or rejects. It's like a race, where the first to the finish line wins.

Real-World Implementation:

// Perform multiple actions and handle the first to complete
const promises = [
  Promise.resolve(1),
  Promise.resolve(2),
  Promise.resolve(3)
];
Promise.race(promises).then((result) => {
  console.log(`The first result is ${result}.`);
});

Potential Application:

This is useful for situations where you want to handle multiple operations concurrently and respond to the first to complete.

5. Promise.allSettled

Simplified Explanation:

This method returns a promise that resolves when all the promises in the array have settled, regardless of whether they resolved or rejected. It's like waiting for everyone in a group to finish their tasks, even if some fail.

Real-World Implementation:

// Perform multiple actions and handle all results
const promises = [
  Promise.resolve(1),
  Promise.reject(2),
  Promise.resolve(3)
];
Promise.allSettled(promises).then((results) => {
  console.log(results); // Contains both resolved and rejected results
});

Potential Application:

This is useful for situations where you need to track the status of multiple promises and handle them collectively, even if some fail.

Promise.props()

Promise.props()

Simplified Explanation:

Imagine you have a bunch of tasks that you want to run at the same time. Instead of waiting for each task to finish before starting the next one, you can use Promise.props() to run them all concurrently and get the results back as a single object.

How it Works:

Promise.props() takes an object as input, where each key is a property name and each value is a promise. It returns a new promise that resolves to an object with the same keys as the input object, but the values are the resolved values of the corresponding promises.

Code Snippet:

const task1 = Promise.resolve(1);
const task2 = Promise.resolve(2);
const task3 = Promise.resolve(3);

Promise.props({
  num1: task1,
  num2: task2,
  num3: task3
})
.then((result) => {
  console.log(result); // { num1: 1, num2: 2, num3: 3 }
});

Real-World Use Cases:

  • Fetching Multiple API Endpoints Concurrently: Retrieve data from several APIs simultaneously, allowing for faster loading times.

  • Collecting Results from Database Queries: Run multiple database queries in parallel to improve performance and avoid sequential bottlenecks.

  • Processing Input Fields in a Form: Validate user inputs from different fields at the same time, providing a better user experience.

Potential Applications:

  • Web Development: Asynchronous page loading, data fetching, and form validation.

  • Data Analysis: Simultaneous processing of multiple datasets.

  • Cloud Computing: Orchestration of distributed tasks and parallel workloads.

Promise.map()

Promise.map()

What is it?

Promise.map() is a function that takes an array and a mapper function, and returns a promise that resolves to an array of the results of the mapped function.

How does it work?

Promise.map() iterates over the array, calling the mapper function on each element. Each call to the mapper function returns a promise, and Promise.map() waits for all of these promises to resolve before resolving its own promise.

Syntax:

Promise.map(array, mapperFunction)

Parameters:

  • array: The array to iterate over.

  • mapperFunction: The function to call on each element of the array.

Returns:

  • A promise that resolves to an array of the results of the mapper function.

Example 1:

Promise.map([1, 2, 3], (num) => num * 2)
  .then((results) => {
    console.log(results); // [2, 4, 6]
  });

In this example, Promise.map() is used to iterate over the array [1, 2, 3] and multiply each element by 2. The result is an array of 3 elements: [2, 4, 6].

Example 2:

const fetchUsers = (userIds) => Promise.map(userIds, (userId) => fetchUser(userId));

In this example, Promise.map() is used to fetch a user for each user ID in the userIds array. The fetchUser function is expected to return a promise that resolves to the user object. The result of Promise.map() will be an array of promises, one for each user.

Potential applications:

Promise.map() can be used in a variety of real-world applications, such as:

  • Fetching data from multiple sources

  • Processing data in parallel

  • Validating data

  • Generating reports

Real-world complete code implementations:

Example 1: Fetching data from multiple sources

const fetchUsers = (userIds) => Promise.map(userIds, (userId) => fetchUser(userId));

fetchUsers([1, 2, 3])
  .then((users) => {
    console.log(users); // [user1, user2, user3]
  });

Example 2: Processing data in parallel

const processData = (data) => Promise.resolve(data * 2);

Promise.map([1, 2, 3], processData)
  .then((results) => {
    console.log(results); // [2, 4, 6]
  });

Configuration Options

Concurrency:

  • concurrency: Sets the maximum number of concurrent operations.

  • Promise.config.setWarnings: Sets the warning level for unhandled rejections.

  • Promise.config.longStackTraces: Enables long stack traces for rejected promises.

Error Handling:

  • Promise.onPossiblyUnhandledRejection: Registers a global error handler for unhandled rejections.

  • Promise.onUnhandledRejection: Triggers an event when an unhandled rejection occurs.

  • Promise.try: Creates a Promise that returns the result of a function or throws an error.

Cancellation:

  • Promise.resolve: Creates a resolved Promise with a specified value.

  • Promise.reject: Creates a rejected Promise with a specified value.

  • Promise.cancel: Cancels a Promise if it is pending and returns a cancelled Promise.

Debugging:

  • Promise.config.stackHook: Customizes the stack trace format for rejected promises.

  • Promise.config.warnings: Sets the warning level for potential errors.

  • Promise.config.useInspect: Enables inspection of Promises for debugging.

Real-World Applications:

  • Concurrency: Limiting concurrent requests to prevent server overload or slowdowns.

  • Error Handling: Catching and handling errors gracefully in asynchronous code, improving stability and user experience.

  • Cancellation: Interrupting asynchronous operations when necessary, such as when a user navigates away from a web page.

  • Debugging: Tracing errors and performance issues in asynchronous code, making development and troubleshooting easier.

Complete Code Example:

// Set concurrency to 3
Promise.config.concurrency = 3;

// Set warning level for unhandled rejections to 'warning'
Promise.config.setWarnings('warning');

// Register a global error handler
Promise.onPossiblyUnhandledRejection((err) => {
  console.error('Unhandled error:', err);
});

// Create a Promise that calls a function
const promise = Promise.try(() => {
  // Do something
});

// Cancel the Promise if it is pending
promise.cancel();
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