JS string contain substring

In order to check whether a substring is included in a string in Javascript you can use the following two ways:

indexOf()

The most traditional way is to use the indexOf() method against a string. This method returns the index (number) of the found substring or -1 if the substring is not part of the given string. For example the returned value of “st” in “tester” is 2.

includes()

Since ECMAScript 6 the includes() method is available which returns either true or false, if the substring will be found inside the given string.