how to get a part of a string in javascript code example

Example 1: get part of string javascript

var str="123 - aaaaa"
var num = str.slice(0,3) //num="123"
var name= str.slice(6) //name="aaaaa"

Example 2: reactjs cut part of string

var str = "Hello world!";

var res = str.substring(1, 4);

// res value is "ell"