how to use concatenation string as a variable 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: how to concatenate strings and variables in javascript

const helloName = name => `Hello ${name}!`