URL Parser

A URL (Uniform Resource Locator) is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. Defined in RFC 3986, a URL is composed of several distinct parts, each serving a precise purpose. The scheme (protocol) identifies the access mechanism: HTTP for plain web traffic, HTTPS for encrypted traffic, FTP for file transfers, and dozens of others. The authority section — comprising an optional username and password, the host, and an optional port — tells the client where to connect and how to authenticate.

The path component identifies the specific resource on the server, following the same hierarchical structure as a Unix file system. The query string, introduced by a question mark, carries additional parameters as key-value pairs separated by ampersands. Query strings are how web applications pass state to servers — they power search terms, pagination, filters, tracking codes, and API parameters. The fragment identifier, prefixed by a hash, is never sent to the server; it is processed entirely by the browser to scroll to an element or update client-side routing in single-page applications.

Understanding URL structure is essential for web development, API integration, security analysis, and debugging. Developers routinely need to inspect URLs to verify routing, check parameter encoding, debug authentication headers embedded in connection strings, or extract the origin for CORS configuration. Security researchers analyse URLs to detect open redirects, parameter injection vectors, and subdomain takeover candidates.

The browser's native URL API (window.URL / WHATWG URL Standard) provides a spec-compliant, encoding-aware parser that correctly handles international domain names, percent-encoded characters, and non-standard port numbers. Using it means edge cases — trailing slashes, empty query strings, IPv6 literal addresses — are handled exactly as browsers handle them.