# v8
***
**1. Server-Side Rendering (SSR)**
```javascript
const express = require('express');
const path = require('path');
const app = express();
app.get('/', async (req, res) => {
const { renderToString } = require('react-dom/server');
const App = require('./App.js').default;
const html = renderToString();
res.send(`
My App
${html}
`);
});
app.use(express.static(path.join(__dirname, 'public')));
app.listen(3000);
```
**2. Client-Side Routing**
```javascript
import { BrowserRouter as Router, Route, Link } from 'react-router-dom';
function App() {
return (
);
}
function Home() { return Home
; }
function About() { return About
; }
function Contact() { return Contact
; }
export default App;
```
**3. Asynchronous Programming**
```javascript
const fs = require('fs');
const readFileAsync = async (path) => {
return new Promise((resolve, reject) => {
fs.readFile(path, 'utf8', (err, data) => {
if (err) {
reject(err);
} else {
resolve(data);
}
});
});
};
readFileAsync('file.txt').then((data) => {
console.log(data);
}).catch((err) => {
console.error(err);
});
```
**4. Database Connectivity (MongoDB)**
```javascript
const MongoClient = require('mongodb').MongoClient;
const client = new MongoClient('mongodb://localhost:27017');
async function connect() {
await client.connect();
const db = client.db('my-database');
const collection = db.collection('my-collection');
const result = await collection.insertOne({ name: 'John Doe' });
console.log(`A document was inserted with the _id: ${result.insertedId}`);
}
connect().catch(console.error);
```
**5. WebSockets**
```javascript
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', (ws) => {
ws.on('message', (message) => {
console.log(`Received a message: ${message}`);
ws.send(`Hello, ${message}!`);
});
});
```
**6. Image Processing**
```javascript
const sharp = require('sharp');
sharp('input.jpg')
.resize(200, 200)
.toFile('output.jpg', (err, info) => {
if (err) {
console.error(err);
} else {
console.log(`Image resized to ${info.width}x${info.height}`);
}
});
```
**7. Machine Learning (TensorFlow\.js)**
```javascript
const tf = require('@tensorflow/tfjs');
const model = tf.sequential();
model.add(tf.layers.dense({ units: 100, activation: 'relu', inputShape: [10] }));
model.add(tf.layers.dense({ units: 1, activation: 'sigmoid' }));
const xs = tf.randomNormal([100, 10]);
const ys = tf.randomUniform([100, 1]);
model.compile({ loss: 'meanSquaredError', optimizer: 'adam' });
model.fit(xs, ys, { epochs: 100 }).then(() => {
console.log('Model trained!');
});
```
**8. Audio Processing**
```javascript
const Speaker = require('speaker');
const speaker = new Speaker({
channels: 2, // 2 channels
bitDepth: 16, // 16-bit samples
sampleRate: 44100 // 44,100 Hz sample rate
});
speaker.write('Hello, world!');
```
**9. Video Processing**
```javascript
const ffmpeg = require('fluent-ffmpeg');
ffmpeg('input.mp4')
.output('output.mp4')
.videoCodec('libx264')
.audioCodec('aac')
.saveToFile((err) => {
if (err) {
console.error(err);
} else {
console.log('Video transcoded!');
}
});
```
**10. Performance Analysis**
```javascript
const util = require('util');
const benchmark = async () => {
const start = process.hrtime();
await Promise.all([
// Run multiple asynchronous tasks
]);
const end = process.hrtime(start);
console.log(`Benchmark took ${util.inspect(end, { depth: null })} seconds to complete.`);
};
benchmark();
```
**11. Unit Testing**
```javascript
const assert = require('assert');
const sum = (a, b) => a + b;
describe('Sum function', () => {
it('should return the sum of two numbers', () => {
assert.strictEqual(sum(1, 2), 3);
});
it('should return 0 when one of the numbers is 0', () => {
assert.strictEqual(sum(0, 2), 0);
});
});
```
**12. End-to-End Testing**
```javascript
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://example.com');
await page.screenshot({ path: 'screenshot.png' });
await browser.close();
})();
```
**13. Performance Profiling**
```javascript
const { performance } = require('perf_hooks');
const measurePerformance = (fn, ...args) => {
const start = performance.now();
const result = fn(...args);
const end = performance.now();
console.log(`Function took ${end - start} milliseconds to execute.`);
return result;
};
measurePerformance(sum, 1, 2);
```
**14. Code Coverage**
```javascript
const nyc = require('nyc');
nyc.instrument({
cwd: process.cwd(),
all: true
});
require('./main.js');
nyc.report();
```
**15. Static Code Analysis**
```javascript
const eslint = require('eslint');
const linter = new eslint.Linter();
const results = linter.verify('./main.js', {
rules: {
// Specify the rules to check
}
});
results.map((result) => {
console.log(`Line ${result.line}: ${result.message}`);
});
```
**16. Build Tooling (Webpack)**
```javascript
const webpack = require('webpack');
const config = {
entry: './main.js',
output: {
path: path.resolve(__dirname, 'dist'),
filename: 'main.js'
},
module: {
rules: [
// Specify the loaders and rules for transpiling, linting, etc.
]
},
plugins: [
// Specify the plugins for optimizing, etc.
]
};
webpack(config, (err, stats) => {
if (err) {
console.error(err);
} else {
console.log(stats.toString());
}
});
```
**17. Test Runner (Mocha)**
```javascript
const assert = require('assert');
const Mocha = require('mocha');
const mocha = new Mocha();
mocha.addFile('./test.js');
mocha.run((failures) => {
process.exitCode = failures ? 1 : 0;
});
```
**18. Debugger (Node.js Inspector)**
```javascript
const inspector = require('inspector');
inspector.open(9229, '0.0.0.0', true);
```
**19. REPL (Node.js REPL)**
```javascript
const repl = require('repl');
repl.start({ prompt: '> ' });
```
**20. Context Isolation**
```javascript
const vm = require('vm');
const context = vm.createContext({
console: console
});
vm.runInContext('console.log("Hello, world!")', context);
```
**21. Sandboxing**
```javascript
const sandbox = require('sandbox');
const sandboxedFn = sandbox.compile('(a, b) => a + b', { timeout: 5000 });
console.log(sandboxedFn(1, 2));
```
**22. Native Add-ons**
```C++
#include
namespace demo {
using Nan::New;
using Nan::Set;
NAN_METHOD(Hello) {
info.GetReturnValue().Set(New("Hello, world!").ToLocalChecked());
}
NAN_MODULE_INIT(Init) {
Set(target, New("hello").ToLocalChecked(),
New(Hello)->GetFunction());
}
NODE_MODULE(addon, Init)
} // namespace demo
```
**23. Internationalization**
```javascript
const i18n = require('i18n');
i18n.configure({
locales: ['en', 'es'],
defaultLocale: 'en',
directory: path.join(__dirname, 'locales')
});
const message = i18n.__('Hello, world!');
console.log(message);
```
**24. HTTP Proxy**
```javascript
const httpProxy = require('http-proxy');
const proxy = httpProxy.createProxyServer({});
httpProxy.web(request, response, { target: 'http://example.com' });
```
**25. WebSocket Proxy**
```javascript
const WebSocket = require('ws');
const httpProxy = require('http-proxy');
const wss = new WebSocket.Server({ port: 8080 });
const proxy = httpProxy.createProxyServer({ ws: true });
wss.on('connection', (ws, req) => {
proxy.web(ws, req, { target: 'ws://example.com' });
});
```
**26. Rate Limiting**
```javascript
const rateLimit = require('express-rate-limit');
const app = express();
const limiter = rateLimit({
windowMs: 15 * 60 * 1000, // 15 minutes
max: 100 // limit each IP to 100 requests per windowMs
});
app.use(limiter);
```
**27. Authentication**
```javascript
const passport = require('passport');
const app = express();
app.use(passport.initialize());
app.use(passport.session());
passport.use(new LocalStrategy((username, password, done) => {
// Lookup the user in the database
// ...
// Return done(null, user) if the user is authenticated,
// or done(null, false) if the user is not authenticated.
}));
```
**28. Caching**
```javascript
const redis = require('redis');
const client = redis.createClient();
client.set('key', 'value', (err, reply) => {
if (err) {
console.error(err);
} else {
console.log(`Value set: ${reply}`);
}
});
client.get('key', (err, reply) => {
if (err) {
console.error(err);
} else {
console.log(`Value fetched: ${reply}`);
}
});
```
**29. Data Validation**
```javascript
const Ajv = require('ajv');
const ajv = new Ajv();
const schema = {
type: 'object',
properties: {
name: { type: 'string' },
age: { type: 'number' }
},
required: ['name', 'age']
};
const validate = ajv.compile(schema);
const data = { name: 'John Doe', age: 30 };
const valid = validate(data);
if (valid) {
console.log('Data is valid');
} else {
console.log('Data is invalid: ', validate.errors);
}
```
**30. Input Sanitation**
```javascript
const sanitizeHtml = require('sanitize-html');
const sanitizedHtml = sanitizeHtml('');
console.log(`Sanitized HTML: ${sanitizedHtml}`);
```
**31. Output Escaping**
```javascript
const escapeHtml = require('escape-html');
const escapedHtml = escapeHtml('');
console.log(`Escaped HTML: ${escapedHtml}`);
```
**32. Error Handling**
```javascript
try {
// Code that may throw an error
} catch (error) {
// Handle the error
} finally {
// Code that will always run, regardless of whether an error was thrown
}
```
**33. Promises**
```javascript
const promise = new Promise((resolve, reject) => {
// Code that may take some time to complete
if (successful) {
resolve('Success');
} else {
reject('Failure');
}
});
promise.then((result) => {
console.log(result);
}).catch((error) => {
console.error(error);
});
```
**34. Async/Await**
```javascript
const fetch = require('node-fetch');
async function getGithubUser(username) {
const response = await fetch(`https://api.github.com/users/${username}`);
if (!response.ok) {
throw new Error(`Error: ${response.status} ${response.statusText}`);
}
return await response.json();
}
getGithubUser('username').then((user) => {
console.log(`User: ${user.name}`);
}).catch((error) => {
console.error(error);
});
```
**35. Generators**
```javascript
function* fibonacci() {
let [a, b] = [0, 1];
while (true) {
yield a;
[a, b] = [b, a + b];
}
}
for (const num of fibonacci()) {
console.log(num);
if (num > 100) {
break;
}
}
```
**36. Streams**
```javascript
const fs = require('fs');
const readableStream = fs.createReadStream('input.txt');
const writableStream = fs.createWriteStream('output.txt');
readableStream.pipe(writableStream);
```