javascript add to string

//This method adds two or more strings and returns a new single string.

let str1 = new String( "This is string one" ); 
let str2 = new String( "This is string two" ); 
let str3 = str1.concat(str2.toString());
console.log("str1 + str2 : "+str3)

output:
str1 + str2 : This is string oneThis is string two

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.

var str1 = "Hello ";
var str2 = "world!";
var res = str1.concat(str2);
console.log(res);

var aString="";
aString.concat(string2, string3, string4,......, stringN)

var totn_string = '';

console.log(totn_string.concat('Tech','On','The','Net'));

//The following will be output to the web browser console log:

TechOnTheNet

//Below code prints It's alright.
var x = 'It\'s alright.';

var a = "Hello";
var b = "World";
var c = a + " " + b;

    var dest = new String("");
    var src = new String("aze");
    var ar = new Array();
    ...
    ar.push(src);
    ar.push(src);
    ...
    dest = ar.join("");

var aString="";
aString.concat(value1, value2, ... value_n);

var s = 'hell'
s = s + 'o'