String

`String.prototype.includes`

Determines whether one string may be found within another string, returning true or false

Syntax

JavaScript

string.includes(searchString, position?)

Parameters

Parameter	Type	Description
searchString	string	A string to be searched for
position	number	Position to begin searching from

Return Value

true if the search string is found, false otherwise

Examples

Basic Usage

const str = 'Hello World';
console.log(str.includes('World')); // true
console.log(str.includes('world')); // false

Practical Example

const url = 'https://example.com/api/users';
if (url.includes('/api/')) {
  console.log('API endpoint detected');
}

Advanced Usage

const sentence = 'The quick brown fox';
console.log(sentence.includes('quick', 5)); // false

Understanding String.prototype.includes

The String.prototype.includes method in JavaScript determines whether one string may be found within another string, returning true or false. It belongs to the String object and is one of the most widely used methods for working with string values in modern JavaScript and TypeScript applications.

The method signature is string.includes(searchString, position?). It accepts 2 parameters: searchString, position. When called, it returns true if the search string is found, false otherwise. Understanding when and how to use includes() helps you write more expressive, readable code.

Common use cases for String.prototype.includes include data transformation, input validation, API response processing, and building reusable utility functions. It works well alongside related methods like string-indexof, string-startswith, string-endswith, enabling you to chain operations together for complex data manipulation pipelines.

Browser support for String.prototype.includes is excellent across all modern browsers including Chrome, Firefox, Safari, and Edge. It is also fully supported in Node.js and Deno. For older environments, transpilation with Babel or a polyfill may be needed.