String.prototype.concat()

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

Syntax

str.concat(str2 [, ...strN])

Parameters

str2 [, ...strN]
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.

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"

Performance

It is strongly recommended that the assignment operators (+, +=) are used instead of the concat() method. 
According to this performance test, the assignment operators are several times faster.

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 Latest Draft (ECMA-262)
The definition of 'String.prototype.concat' in that specification.		 Draft

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
concatChrome Full support 1Edge Full support 12Firefox Full support 1IE Full support 4Opera Full support YesSafari Full support 1WebView Android Full support 1Chrome Android Full support 18Firefox Android Full support 4Opera Android Full support YesSafari iOS Full support 1Samsung Internet Android Full support 1.0nodejs Full support Yes

Legend

Full support  
Full support

See also

Related Topics
  1. Standard built-in objects
  2. String
  3. Properties
    1. String length
    2. String.prototype
  4. Methods
    1. String.fromCharCode()
    2. String.fromCodePoint()
    3. String.prototype.anchor()
    4. String.prototype.big()
    5. String.prototype.blink()
    6. String.prototype.bold()
    7. String.prototype.charAt()
    8. String.prototype.charCodeAt()
    9. String.prototype.codePointAt()
    10. String.prototype.concat()
    11. String.prototype.endsWith()
    12. String.prototype.fixed()
    13. String.prototype.fontcolor()
    14. String.prototype.fontsize()
    15. String.prototype.includes()
    16. String.prototype.indexOf()
    17. String.prototype.italics()
    18. String.prototype.lastIndexOf()
    19. String.prototype.link()
    20. String.prototype.localeCompare()
    21. String.prototype.match()
    22. String.prototype.matchAll()
    23. String.prototype.normalize()
    24. String.prototype.padEnd()
    25. String.prototype.padStart()
    26. String.prototype.quote()
    27. String.prototype.repeat()
    28. String.prototype.replace()
    29. String.prototype.search()
    30. String.prototype.slice()
    31. String.prototype.small()
    32. String.prototype.split()
    33. String.prototype.startsWith()
    34. String.prototype.strike()
    35. String.prototype.sub()
    36. String.prototype.substr()
    37. String.prototype.substring()
    38. String.prototype.sup()
    39. String.prototype.toLocaleLowerCase()
    40. String.prototype.toLocaleUpperCase()
    41. String.prototype.toLowerCase()
    42. String.prototype.toSource()
    43. String.prototype.toString()
    44. String.prototype.toUpperCase()
    45. String.prototype.trim()
    46. String.prototype.trimEnd()
    47. String.prototype.trimStart()
    48. String.prototype.valueOf()
    49. String.prototype[@@iterator]()
    50. String.raw()
  5. Inheritance:
  6. Function
  7. Properties
    1. Function.arguments
    2. Function.arity
    3. Function.caller
    4. Function.displayName
    5. Function.length
    6. Function.name
    7. Function.prototype
  8. Methods
    1. Function.prototype.apply()
    2. Function.prototype.bind()
    3. Function.prototype.call()
    4. Function.prototype.isGenerator()
    5. Function.prototype.toSource()
    6. Function.prototype.toString()
  9. Object
  10. Properties
    1. Object.prototype.__count__
    2. Object.prototype.__noSuchMethod__
    3. Object.prototype.__parent__
    4. Object.prototype.__proto__
    5. Object.prototype.constructor
  11. Methods
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.unwatch()
    12. Object.prototype.valueOf()
    13. Object.prototype.watch()
    14. Object.setPrototypeOf()