How to check whether a string contains a substring in JavaScript?

Question

Usually I would expect a `String.contains()` method, but there doesn't seem to be one. What is a reasonable way to check for this?

Accepted Answer

ECMAScript 6 introduced `String.prototype.includes`:

```
const string = "foo";
const substring = "oo";

console.log(string.includes(substring)); // true
```

`String.prototype.includes` is case-sensitive and is not supported by Internet Explorer without a polyfill.

In ECMAScript 5 or older environments, use `String.prototype.indexOf`, which returns -1 when a substring cannot be found:

```
var string = "foo";
var substring = "oo";

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

Solution