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arguments
is an Array
-like object accessible inside functions that contains the values of the arguments passed to that function.
Note: If you're writing ES6 compatible code, then rest parameters should be preferred.
Note: “Array-like” means that arguments
has a length
property and properties indexed from zero, but it doesn't have Array
's built-in methods like forEach()
and map()
. See §Description for details.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Syntax
arguments
Description
The arguments
object is a local variable available within all non-arrow functions. You can refer to a function's arguments inside that function by using its arguments
object. It has entries for each argument the function was called with, with the first entry's index at 0.
For example, if a function is passed 3 arguments, you can access them as follows:
arguments[0] // first argument arguments[1] // second argument arguments[2] // third argument
Each argument can also be set or reassigned:
arguments[1] = 'new value';
The arguments
object is not an Array
. It is similar, but does not have any Array
properties except length
. For example, it does not have the pop()
method. However, it can be converted to a real Array
:
var args = Array.prototype.slice.call(arguments); // Using an array literal is shorter than above but allocates an empty array var args = [].slice.call(arguments);
As you can do with any Array-like object, you can use ES2015's Array.from()
method or spread syntax to convert arguments
to a real Array:
var args = Array.from(arguments); var args = [...arguments];
The arguments
object is useful for functions called with more arguments than they are formally declared to accept. This technique is useful for functions that can be passed a variable number of arguments, such as Math.min()
. This example function accepts any number of string arguments and returns the longest one:
function longestString() { var longest = ''; for (var i=0; i < arguments.length; i++) { if (arguments[i].length > longest.length) { longest = arguments[i]; } } return longest; }
You can use arguments.length
to count how many arguments the function was called with. If you instead want to count how many parameters a function is declared to accept, inspect that function's length
property.
Using typeof
with Arguments
The typeof
operator returns 'object'
when used with arguments
console.log(typeof arguments); // 'object'
The type of individual arguments can be determined by indexing arguments
:
console.log(typeof arguments[0]); // returns the type of the first argument
Properties
arguments.callee
- Reference to the currently executing function that the arguments belong to.
arguments.caller
- Reference to the function that invoked the currently executing function.
arguments.length
- The number of arguments that were passed to the function.
arguments[@@iterator]
- Returns a new
Array
iterator object that contains the values for each index in thearguments
.
Examples
Defining a function that concatenates several strings
This example defines a function that concatenates several strings. The function's only formal argument is a string containing the characters that separate the items to concatenate.
function myConcat(separator) { var args = Array.prototype.slice.call(arguments, 1); return args.join(separator); }
You can pass as many arguments as you like to this function. It returns a string list using each argument in the list:
// returns "red, orange, blue" myConcat(', ', 'red', 'orange', 'blue'); // returns "elephant; giraffe; lion; cheetah" myConcat('; ', 'elephant', 'giraffe', 'lion', 'cheetah'); // returns "sage. basil. oregano. pepper. parsley" myConcat('. ', 'sage', 'basil', 'oregano', 'pepper', 'parsley');
Defining a function that creates HTML lists
This example defines a function that creates a string containing HTML for a list. The only formal argument for the function is a string that is "u
" if the list is to be unordered (bulleted), or "o
" if the list is to be ordered (numbered). The function is defined as follows:
function list(type) { var html = '<' + type + 'l><li>'; var args = Array.prototype.slice.call(arguments, 1); html += args.join('</li><li>'); html += '</li></' + type + 'l>'; // end list return html; }
You can pass any number of arguments to this function, and it adds each argument as a list item to a list of the type indicated. For example:
var listHTML = list('u', 'One', 'Two', 'Three'); /* listHTML is: "<ul><li>One</li><li>Two</li><li>Three</li></ul>" */
Rest, default, and destructured parameters
The arguments
object can be used in conjunction with rest, default, and destructured parameters.
function foo(...args) { return args; } foo(1, 2, 3); // [1,2,3]
While the presence of rest, default, or destructured parameters does not alter the behavior of the arguments
object in strict mode code, there is a subtle difference for non-strict code.
If a non-strict function does not contain rest, default, or destructured parameters, then the values in the arguments
object do change in sync with the values of the argument variables. See the code below:
function func(a) { arguments[0] = 99; // updating arguments[0] also updates a console.log(a); } func(10); // 99
and
function func(a) { a = 99; // updating a also updates arguments[0] console.log(arguments[0]); } func(10); // 99
When a non-strict function does contain rest, default, or destructured parameters, then the values in the arguments
object do not track the values of the arguments. Instead, they reflect the arguments provided when the function was called:
function func(a = 55) { arguments[0] = 99; // updating arguments[0] does not also update a console.log(a); } func(10); // 10
and
function func(a = 55) { a = 99; // updating a does not also update arguments[0] console.log(arguments[0]); } func(10); // 10
and
// An untracked default parameter function func(a = 55) { console.log(arguments[0]); } func(); // undefined
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.1 |
ECMAScript 5.1 (ECMA-262) The definition of 'Arguments Object' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Arguments Exotic Objects' in that specification. |
Standard | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Arguments Exotic Objects' in that specification. |
Draft |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
arguments | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
callee | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 6 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
caller | Chrome No support No | Edge No support No | Firefox No support No | IE No support 3 — 9 | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
length | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
@@iterator | Chrome Full support 52 | Edge Full support 12 | Firefox Full support 46 | IE No support No | Opera Full support Yes | Safari Full support 9 | WebView Android Full support 52 | Chrome Android Full support 52 | Firefox Android Full support 46 | Opera Android Full support Yes | Safari iOS Full support 9 | Samsung Internet Android Full support 6.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
- Non-standard. Expect poor cross-browser support.
- Non-standard. Expect poor cross-browser support.
- Deprecated. Not for use in new websites.
- Deprecated. Not for use in new websites.