String.prototype.concat()
The concat() method combines the text of two or more strings and returns a new string.
Syntax
str.concat(string2[,..., stringN]);
Parameters
string2...string*N* The strings which are to be concatenated to this String.
Description
The concat() method combines the text of two or more strings and returns the concatenated string. It does not modify the original strings.
Examples
Concatenating strings
var str1 = "Hello";
var str2 = "World";
console.log(str1.concat(str2));
// Console will output: HelloWorld
var str2 = "Hello, ";
console.log(str2.concat(" Welcome ", "to FCC."));
// Console will output: Hello, Welcome to FCC.
Source MDN