how append string in js code example

Example 1: string concat javascript

//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

Example 2: string concat in js

let string1 = "Hello"
let string2 = "World"

let finalString = string1 + ", " + string2 + "!" // Hello, World!