String.prototype.concat()

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

Syntax

concat(str1)
concat(str1, str2)
concat(str1, str2, ... , strN)

Parameters

strN
One or more strings to concatenate to str.

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. Changes to the original string or the returned string don't affect the other.

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

Performance

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

Examples

Using concat()

The following example combines strings into a new string.

let hello = 'Hello, '
console.log(hello.concat('Kevin', '. Have a nice day.'))
// Hello, Kevin. Have a nice day.

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

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

Specifications

Specification
ECMAScript Language Specification (ECMAScript)
# sec-string.prototype.concat

Browser compatibility

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See also