The simplest way is with the includes method.

'some big string'.includes('big'); // returns true
'some big string'.includes('Big'); // returns false

The includes method is only available on browser that support ES6. To work with older browsers, you can use indexOf. If it cannot find the substring, it returns -1:

'some big string'.indexOf('big') !== -1; // returns true
'some big string'.indexOf('Big') !== -1; // returns false

Notice you can also use indexOf to get the index of the first substring found.

'some big string'.indexOf('s'); // returns 0
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