string.concat

The concat() method combines the text of one or more strings and returns a new string.

Syntax

str.concat(string2[, string3, ..., stringN])

Parameters

string2...stringN

Strings to concatenate to this string.

Return value

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

Description

The concat() function combines the text from one or more strings and returns a new string. Changes to the text in one string do not affect the other string.

Examples

Using concat()

The following example combines strings into a new string.

var hello = 'Hello, ';
console.log(hello.concat('Kevin', ' have a nice day.'));
/* Hello, Kevin have a nice day. */

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

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

Performance

It is strongly recommended that assignment operators (+, +=) are used instead of the concat() method. See this performance test.

Specifications

Specification	Status	Comment
ECMAScript 3rd Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262) The definition of 'String.prototype.concat' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'String.prototype.concat' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'String.prototype.concat' in that specification.	Draft

Browser compatibility

See also

• Array.prototype.concat()
• Assignment operators