includes() String Method in JavaScript

javascript string includes()

The javascript string includes() method (String.prototype.includes) provides a simple, readable way to check whether one string contains another. It returns a boolean: true when the substring is found and false otherwise. This ES6 string method is commonly used when you need to test if a string contains a given substring in JavaScript.

Syntax

str.includes(searchString[, position])

Parameters:

• searchString — the substring you want to find.
• position (optional) — the index at which to start searching (default is 0).

Basic example

var word = "bravery";
console.log(word.includes("rave")); // true

Case sensitivity

The includes() method is case-sensitive. That means "hi" and "Hi" are different:

const greetings = "Hi Sammy ~";
console.log(greetings.includes("hi")); // false
console.log(greetings.includes("Hi")); // true

Ignoring case

To check if a javascript string contains a substring regardless of case, normalize both strings first:

const haystack = "JavaScript Rocks";
const needle = "javascript";
console.log(haystack.toLowerCase().includes(needle.toLowerCase())); // true

Start position parameter

You can supply a start index to search from a specific position in the string:

const phrase = "hello world";
console.log(phrase.includes("world", 6)); // true
console.log(phrase.includes("world", 7)); // false

Difference between includes() and indexOf()

• includes() — returns a boolean (true/false). Easier to read when you only need to know existence (js includes string).
• indexOf() — returns the index of the substring or -1 if not found. Useful when you need the position.

When to use includes()

• Quick checks to determine if one string contains another (javascript string contains).
• Readable conditional checks: if (str.includes(substr)) { ... }
• When you want a boolean result without handling -1 from indexOf.

Related string search methods

• String.prototype.indexOf()
• String.prototype.startsWith()
• String.prototype.endsWith()
• RegExp methods: test(), match(), search()

Note: includes() was added in ES6 (ECMAScript 2015). For older environments, include a polyfill or use indexOf() for compatibility.

Quick reference examples

// String.prototype.includes() example
const s = "Learn to search within a string";
console.log(s.includes("search")); // true

// includes() with a start position
console.log(s.includes("Learn", 1)); // false

// javascript includes substring example (case-insensitive)
console.log(s.toLowerCase().includes("SEARCH".toLowerCase())); // true