Checking if a string contains a substring is one of the most common tasks in any programming language.

JavaScript offers different ways to perform this operation.

The most simple one, and also the canonical one going forward, is using the includes() method on a string:

'a nice string'.includes('nice') //true

This method was introduced in ES6/ES2015.

It’s supported in all modern browsers except Internet Explorer:

Browser Support for includes

To use it on all browsers, use Polyfill.io or another dedicated polyfill.

includes() also accepts an optional second parameter, an integer which indicates the position where to start searching for:

'a nice string'.includes('nice') //true
'a nice string'.includes('nice', 3) //false
'a nice string'.includes('nice', 2) //true

Pre-ES6 alternative to includes(): indexOf()

Pre-ES6, the common way to check if a string contains a substring was to use indexOf, which is a string method that return -1 if the string does not contain the substring. If the substring is found, it returns the index of the character that starts the string.

Like includes(), the second parameters sets the starting point:

'a nice string'.indexOf('nice') !== -1 //true
'a nice string'.indexOf('nice', 3) !== -1 //false
'a nice string'.indexOf('nice', 2) !== -1 //true