How do you check whether a string contains a substring?

There are 3 possible ways to check whether a string contains a substring or not,

1. Using includes: ES6 provided String.prototype.includes method to test a string contains a substring

      var mainString = "hello",
        subString = "hell";
      mainString.includes(subString);
      

1. Using indexOf: In an ES5 or older environment, you can use String.prototype.indexOf which returns the index of a substring. If the index value is not equal to -1 then it means the substring exists in the main string.

      var mainString = "hello",
        subString = "hell";
      mainString.indexOf(subString) !== -1;
      

1. Using RegEx: The advanced solution is using Regular expression's test method(RegExp.test), which allows for testing for against regular expressions

      var mainString = "hello",
        regex = /hell/;
      regex.test(mainString);