how to join two strings together in javascript 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: javascript join 2 variables into string

A = 'hello ';
B = 'world!';

// outputs "hello world!"
console.log(A + B);