StringprototypematchAll

String.prototype is the built-in prototype object used as the common ancestor for all string instances in JavaScript. It is defined by the ECMAScript standard and provides the methods and properties that are available on string values reached through either string literals or String objects. When a primitive string is used, the engine temporarily boxes it into a String object so that its methods from String.prototype can be invoked via the usual prototype chain.

Typical members of String.prototype include a range of instance methods such as charAt, charCodeAt, codePointAt, includes, startsWith, endsWith, indexOf, lastIndexOf, match, matchAll, replace, replaceAll, slice, substring, toLowerCase, toUpperCase, trim, split, repeat, padStart, and padEnd, as well as toString and valueOf. In addition, String.prototype supports iteration via Symbol.iterator, which allows strings to be iterated character by character in for-of loops. The length property is a characteristic of string instances rather than a property defined on the prototype itself.

Usage examples illustrate typical behavior: 'hello'.includes('ell') returns true; 'abcdef'.slice(1,3) returns 'bc'; 'Hello'.toLowerCase() returns 'hello'. Strings are immutable; many prototype methods return new strings or other values without altering the original string.

Extensibility and caveats: developers can augment String.prototype with new methods, making them available to all strings. However, modifying built-in prototypes can cause compatibility issues and conflicts with future standards, so such patches are generally discouraged in production code.