how to concatenate a variable on a string js code example

Example 1: how to concatenate strings javascript

var str1 = "Hello ";
var str2 = "world!";
var res = str1.concat(str2);
// does not change the existing strings, but
// returns a new string containing the text
// of the joined strings.

Example 2: concat no and string in javascript

['Hello', ' ', 'World'].join(''); // 'Hello World'