URL Encoder and Decoder in JavaScript / Node.js — Code Examples

URL encoding (percent-encoding) replaces characters that are not allowed in URLs with a percent sign followed by their hexadecimal value. Here is how to encode and decode URL components in each language.

JavaScript has two pairs of functions: encodeURI/decodeURI for full URLs and encodeURIComponent/decodeURIComponent for individual query parameter values.

// Encode a query parameter value (most common use case)
const param = "hello world & foo=bar";
const encoded = encodeURIComponent(param);
console.log(encoded); // hello%20world%20%26%20foo%3Dbar

// Decode
const decoded = decodeURIComponent("hello%20world%20%26%20foo%3Dbar");
console.log(decoded); // hello world & foo=bar

// Encode a full URL (preserves ://?=& structure)
const url = "https://example.com/search?q=hello world";
const encodedUrl = encodeURI(url);
console.log(encodedUrl); // https://example.com/search?q=hello%20world

// Build a query string from an object
const params = new URLSearchParams({ q: "hello world", page: "1" });
console.log(params.toString()); // q=hello+world&page=1
console.log("?" + params.toString());

• Use encodeURIComponent for query parameter values, not encodeURI — encodeURI leaves & = ? / intact.
• URLSearchParams is the modern way to build query strings; it handles encoding automatically.
• encodeURIComponent encodes spaces as %20; URLSearchParams encodes them as + (both are valid in query strings).

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