Question 1

What is a query string and how does it work?

Accepted Answer

A query string is the part of a URL after the ? that contains key-value pairs separated by &. Example: ?name=John&age=30&city=New%20York. Keys and values are percent-encoded: spaces become %20 or +, & in values becomes %26. The server receives the raw query string and parses it into parameters. In JavaScript, new URL(window.location.href).searchParams provides easy access without manual parsing.

Question 2

How do I parse a query string in JavaScript?

Accepted Answer

Use URLSearchParams: const params = new URLSearchParams('?name=John&age=30'); params.get('name') // 'John'. For browser URLs: const params = new URL(window.location.href).searchParams. To iterate: for (const [key, value] of params) {...}. To get all values for a repeated key (arrays): params.getAll('tag'). To build a query string: new URLSearchParams({name:'John', age:30}).toString() → 'name=John&age=30'. Available in all modern browsers and Node.js 10+.

Question 3

How are arrays represented in query strings?

Accepted Answer

There is no standard for arrays in query strings — different frameworks use different conventions. Common formats: repeated keys: ?tag=js&tag=css (parsed by URLSearchParams.getAll()); bracket notation: ?tags[]=js&tags[]=css (PHP style, Rails); dot notation: ?tags.0=js&tags.1=css; JSON-encoded: ?tags=["js","css"]. URLSearchParams handles repeated keys; for bracket notation you need qs library (Node.js) or similar. When designing APIs, repeated keys are the most universally supported.

Question 4

What is the maximum length of a URL and query string?

Accepted Answer

HTTP/1.1 has no specified URL length limit, but servers and browsers impose practical limits. Chrome and Firefox support URLs up to ~2MB. IE limited URLs to 2,048 characters (this became the informal web standard). Apache and Nginx default to 8KB and 4KB for request URI respectively. AWS API Gateway limits query strings to 10KB. As a practical rule: keep URLs under 2,000 characters for broad compatibility. For large data, use POST with a request body instead of GET with a long query string.

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