Substring in JavaScript  

In JavaScript ES6, use

str.includes(substr)

Example

"hello".includes("el");      //returns true.

To make it work on older browsers, you may need to load es6-shim

require('es6-shim')

I prefer using the third party-libraries like Lodash and Underscore.

Lodash:

_.includes('hello', 'el');

Underscore:

_.str.include('hello', 'el');

To do a case-insensitive search, use search() with a regular expression

var str = "Hello World";
var index = str.search(/world/i);        //returns 6

Use the str.indexOf(searchStr) method where searchStr is a string representing the value to search for in the string str.

The return value is the index of the first occurrence of the specified value. It returns -1 if the string is not found.

'Hello World'.indexOf('ello');     //returns 1
'Hello World'.indexOf('Helo');      //returns -1

You can pass an optional second parameter which is the index at which to start the searching forwards in the string.

'Hello World'.indexOf('World', 5);  //returns 6