How to check if a string contains a substring in JavaScript

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With JavaScript ES6 we can leverage the String.prototype.includes method to check if a substring exists within a string. Here's an example:

const string = 'Hello World!';
const substring = 'World';


// true

If you're working with older browsers such as Internet Explorer support for this method can be spotty. We can instead use String.prototype.indexOf:

var string = 'Hello World!';
var substring = 'World';

console.log(string.indexOf(substring) !== -1);

// true