javascript string concatenation

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.var str1 = "Hello ";
var str2 = "world!";
var res = str1.concat(str2);
console.log(res);//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 twoconst helloName = name => `Hello ${name}!`const str1 = 'Hello';
const str2 = 'World';

console.log(str1 + str2);
>> HelloWorld

console.log(str1 + ' ' + str2);
>> Hello Worldvar totn_string = '';

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

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

TechOnTheNet
Source

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