String.prototype.concat()

{{JSRef}} 

The concat() method of {{jsxref("String")}}  values concatenates the string arguments to this string and returns a new string.

{{InteractiveExample("JavaScript Demo: String.concat()")}} 

const str1 = "Hello";
const str2 = "World";

console.log(str1.concat(" ", str2));
// Expected output: "Hello World"

console.log(str2.concat(", ", str1));
// Expected output: "World, Hello"

Syntax

concat(str1)
concat(str1, str2)
concat(str1, str2, /* …, */ strN)

Parameters

• str1, …, strN
  • : One or more strings to concatenate to str. Though technically permitted, calling String.prototype.concat() with no arguments is a useless operation, because it does not result in observable copying (like {{jsxref("Array.prototype.concat()")}} ), since strings are immutable. It should only happen if you are spreading an array of strings as arguments, and that array happens to be empty.

Return value

A new string containing the combined text of the strings provided.

Description

The concat() function concatenates the string arguments to the calling string and returns a new string.

If the arguments are not of the type string, they are converted to string values before concatenating.

The concat() method is very similar to the addition/string concatenation operators (+, +=), except that concat() coerces its arguments directly to strings, while addition coerces its operands to primitives first. For more information, see the reference page for the + operator.

Examples

Using concat()

The following example combines strings into a new string.

const hello = "Hello, ";
console.log(hello.concat("Kevin", ". Have a nice day."));
// Hello, Kevin. Have a nice day.

const greetList = ["Hello", " ", "Venkat", "!"];
"".concat(...greetList); // "Hello Venkat!"

"".concat({}); // "[object Object]"
"".concat([]); // ""
"".concat(null); // "null"
"".concat(true); // "true"
"".concat(4, 5); // "45"

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}} 

See also

• {{jsxref("Array.prototype.concat()")}} 
• Addition (+)