# querystring

***

**1. Parse a Query String into an Object:**

```js
const queryString = require('querystring');
const query = 'name=John&age=30';
const parsedQuery = queryString.parse(query);
// { name: 'John', age: '30' }
```

**2. Serialize an Object into a Query String:**

```js
const queryString = require('querystring');
const obj = { name: 'John', age: 30 };
const serializedQuery = queryString.stringify(obj);
// 'name=John&age=30'
```

**3. Decode a URI-Encoded Query String:**

```js
const queryString = require('querystring');
const encodedQuery = '%3Fname%3DJohn%26age%3D30';
const decodedQuery = queryString.unescape(encodedQuery);
// '?name=John&age=30'
```

**4. Strip Leading and Trailing Spaces from Query Parameters:**

```js
const queryString = require('querystring');
const query = ' name=John  & age=30 ';
const trimmedQuery = queryString.unescape(query.trim());
// 'name=John&age=30'
```

**5. Parse a Query String with Array Values:**

```js
const queryString = require('querystring');
const query = 'user_id[]=1&user_id[]=2&user_id[]=3';
const parsedQuery = queryString.parse(query);
// { user_id: [ '1', '2', '3' ] }
```

**6. Parse a Query String with Nested Objects:**

```js
const queryString = require('querystring');
const query = 'user={name:John,age:30}&address={city:London,country:UK}';
const parsedQuery = queryString.parse(query);
// {
//   user: { name: 'John', age: '30' },
//   address: { city: 'London', country: 'UK' }
// }
```

**7. Encode a Query String for a URL:**

```js
const queryString = require('querystring');
const query = { name: 'John', age: 30 };
const encodedQueryString =queryString.stringify(query);
const url = 'https://example.com?' + encodedQueryString;
// 'https://example.com?name=John&age=30'
```

**8. Parse a Query String from a URL:**

```js
const queryString = require('querystring');
const url = 'https://example.com?name=John&age=30';
const parsedQuery =queryString.parse(url.substring(url.indexOf('?') + 1));
// { name: 'John', age: '30' }
```

**9. Remove Specific Query Parameters from a Query String:**

```js
const queryString = require('querystring');
const query = 'name=John&age=30&gender=male';
const filteredQuery = queryString.parse(query);
delete filteredQuery.gender;
const newQuery = queryString.stringify(filteredQuery);
// 'name=John&age=30'
```

**10. Merge Two Query Strings:**

```js
const queryString = require('querystring');
const query1 = 'name=John&age=30';
const query2 = 'city=London&country=UK';
const mergedQuery = queryString.parse(query1 + '&' + query2);
// { name: 'John', age: '30', city: 'London', country: 'UK' }
```

**11. Convert a Query String to a Buffer:**

```js
const queryString = require('querystring');
const query = 'name=John&age=30';
const buffer = Buffer.from(queryString.parse(query));
// <Buffer 7b 6e 61 6d 65 3d 4a 6f 68 6e 26 61 67 65 3d 33 30 7d>
```

**12. Convert a Query String to a JSON String:**

```js
const queryString = require('querystring');
const query = 'name=John&age=30';
const json = JSON.stringify(queryString.parse(query));
// '{"name":"John","age":"30"}'
```

**13. Parse a Query String with Custom Delimiters:**

```js
const queryString = require('querystring');
const query = 'user,id=1,name=John,age=30';
const parsedQuery = queryString.parse(query, { separator: ',' });
// { user: 'id=1,name=John,age=30' }
```

**14. Parse a Query String with Custom Assignment Operators:**

```js
const queryString = require('querystring');
const query = 'user:id=1:name=John:age=30';
const parsedQuery = queryString.parse(query, { assignment: ':' });
// { user: { id: '1', name: 'John', age: '30' } }
```

**15. Parse a Query String with a Custom Array Format:**

```js
const queryString = require('querystring');
const query = 'user_id=1&user_id=2&user_id=3';
const parsedQuery = queryString.parse(query, { arrayFormat: 'brackets' });
// { user_id: [ '1', '2', '3' ] }
```

**16. Parse a Query String with a Custom Null Value:**

```js
const queryString = require('querystring');
const query = 'user_id=&name=John';
const parsedQuery = queryString.parse(query, { nullValue: null });
// { user_id: null, name: 'John' }
```

**17. Parse a Query String with a Custom Encoding:**

```js
const queryString = require('querystring');
const query = 'user_id=1&name=John%20Doe';
const parsedQuery = queryString.parse(query, { decodeURIComponent: (str) => decodeURIComponent(str.replace('+', ' ')) });
// { user_id: '1', name: 'John Doe' }
```

**18. Parse a Query String with a Custom Array Value Separator:**

```js
const queryString = require('querystring');
const query = 'user_id=1|2|3';
const parsedQuery = queryString.parse(query, { arrayFormat: 'pipe' });
// { user_id: [ '1', '2', '3' ] }
```

**19. Parse a Query String with a Custom Value Separator:**

```js
const queryString = require('querystring');
const query = 'user_id:1,name:John';
const parsedQuery = queryString.parse(query, { separator: ':' });
// { user_id: '1', name: 'John' }
```

**20. Parse a Query String with a Custom Assignment Operator:**

```js
const queryString = require('querystring');
const query = 'user_id=1:name=John';
const parsedQuery = queryString.parse(query, { assignment: ':' });
// { user_id: '1', name: 'John' }
```

**21. Serialize an Object to a Query String with a Custom Delimiter:**

```js
const queryString = require('querystring');
const obj = { user: 'id=1,name=John,age=30' };
const serializedQuery = queryString.stringify(obj, { separator: ',' });
// 'user,id=1,name=John,age=30'
```

**22. Serialize an Object to a Query String with a Custom Assignment Operator:**

```js
const queryString = require('querystring');
const obj = { user: { id: '1', name: 'John', age: '30' } };
const serializedQuery = queryString.stringify(obj, { assignment: ':' });
// 'user:id=1:name=John:age=30'
```

**23. Serialize an Object to a Query String with a Custom Array Format:**

```js
const queryString = require('querystring');
const obj = { user_id: [ '1', '2', '3' ] };
const serializedQuery = queryString.stringify(obj, { arrayFormat: 'brackets' });
// 'user_id=1&user_id=2&user_id=3'
```

**24. Serialize an Object to a Query String with a Custom Null Value:**

```js
const queryString = require('querystring');
const obj = { user_id: null, name: 'John' };
const serializedQuery = queryString.stringify(obj, { nullValue: null });
// 'user_id=&name=John'
```

**25. Serialize an Object to a Query String with a Custom Array Value Separator:**

```js
const queryString = require('querystring');
const obj = { user_id: [ '1', '2', '3' ] };
const serializedQuery = queryString.stringify(obj, { arrayFormat: 'pipe' });
// 'user_id=1|2|3'
```

**26. Serialize an Object to a Query String with a Custom Value Separator:**

```js
const queryString = require('querystring');
const obj = { user_id: '1', name: 'John' };
const serializedQuery = queryString.stringify(obj, { separator: ':' });
// 'user_id:1:name:John'
```

**27. Serialize an Object to a Query String with a Custom Assignment Operator:**

```js
const queryString = require('querystring');
const obj = { user_id: '1', name: 'John' };
const serializedQuery = queryString.stringify(obj, { assignment: ':' });
// 'user_id:1:name:John'
```

**28. Parse a Query String and Validate Parameters:**

```js
const queryString = require('querystring');
const validator = require('validator');

const query = 'name=John&age=30';
const parsedQuery = queryString.parse(query);

if (!validator.isAlpha(parsedQuery.name)) {
  throw new Error('Invalid name');
}
if (!validator.isInt(parsedQuery.age)) {
  throw new Error('Invalid age');
}
```

**29. Use Query Strings to Create Paginated Routes:**

```js
const queryString = require('querystring');

const query = 'page=2';
const parsedQuery = queryString.parse(query);

const limit = 10;
const offset = (parsedQuery.page - 1) * limit;
```

**30. Use Query Strings for Search Functionality:**

```js
const queryString = require('querystring');

const query = 'search=John';
const parsedQuery = queryString.parse(query);

const searchTerm = parsedQuery.search;
```

**31. Use Query Strings for Sorting Data:**

```js
const queryString = require('querystring');

const query = 'sort=name';
const parsedQuery = queryString.parse(query);

const sortField = parsedQuery.sort;
```

**32. Use Query Strings for Filtering Data:**

```js
const queryString = require('querystring');

const query = 'filter=age>30';
const parsedQuery = queryString.parse(query);

const filter = parsedQuery.filter;
```

**33. Use Query Strings for API Authentication:**

```js
const queryString = require('querystring');

const query = 'access_token=12345';
const parsedQuery = queryString.parse(query);

const accessToken = parsedQuery.access_token;
```

**34. Use Query Strings for Tracking User Activity:**

```js
const queryString = require('querystring');

const query = 'utm_source=google&utm_medium=cpc&utm_campaign=search';
const parsedQuery = queryString.parse(query);

const utmSource = parsedQuery.utm_source;
const utmMedium = parsedQuery.utm_medium;
const utmCampaign = parsedQuery.utm_campaign;
```

**35. Use Query Strings for Error Handling:**

```js
const queryString = require('querystring');

const query = 'error=404';
const parsedQuery = queryString.parse(query);

const error = parsedQuery.error;
```

**36. Use Query Strings for Debugging:**

```js
const queryString = require('querystring');

const query = 'debug=true';
const parsedQuery = queryString.parse(query);

const debug = parsedQuery.debug;
```