--- title: Arguments object slug: Web/JavaScript/Reference/Functions/arguments tags: - Functions - JavaScript - NeedsTranslation - TopicStub - arguments translation_of: Web/JavaScript/Reference/Functions/arguments ---

The arguments object is an Array-like object corresponding to the arguments passed to a function.

Syntax

arguments

Description

The arguments object is a local variable available within all functions. arguments as a property of Function can no longer be used.

You can refer to a function's arguments within the function by using the arguments object. This object contains an entry for each argument passed to the function, the first entry's index starting at 0. For example, if a function is passed three arguments, you can refer to the argument as follows:

arguments[0]
arguments[1]
arguments[2]

The arguments can also be set:

arguments[1] = 'new value';

The arguments object is not an {{jsxref("Array")}}. It is similar to an Array, 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);

Important: You should not slice on arguments because it prevents optimizations in JavaScript engines (V8 for example). Instead, try constructing a new array by iterating through the arguments object. More information.

If Array generics are available, one can use the following instead:

var args = Array.slice(arguments);

The arguments object is available only within a function body. Attempting to access the arguments object outside a function declaration results in an error.

You can use the arguments object if you call a function with more arguments than it is formally declared to accept. This technique is useful for functions that can be passed a variable number of arguments. You can use arguments.length to determine the number of arguments passed to the function, and then process each argument by using the arguments object. (To determine the number of arguments declared when a function was defined, use the Function.length property.)

Properties

arguments.callee: Reference to the currently executing function.
arguments.caller {{ Obsolete_inline() }}: Reference to the function that invoked the currently executing function.
arguments.length: Reference to the number of arguments passed to the function.

Examples

Defining a function that concatenates several strings

This example defines a function that concatenates several strings. The only formal argument for the function is a string that specifies the characters that separate the items to concatenate. The function is defined as follows:

function myConcat(separator) {
  var args = Array.prototype.slice.call(arguments, 1);
  return args.join(separator);
}

You can pass any number of arguments to this function, and it creates a list using each argument as an item 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 result = "<" + type + "l><li>";
  var args = Array.prototype.slice.call(arguments, 1);
  result += args.join("</li><li>");
  result += "</li></" + type + "l>"; // end list

  return result;
}

You can pass any number of arguments to this function, and it adds each argument as an 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 parameters, default parameters or destructured parameters.

function foo(...args) {
  return arguments;
}
foo(1, 2, 3); // { "0": 1, "1": 2, "2": 3 }

However, in non-strict functions, a mapped arguments object is only provided if the function does not contain any rest parameters, any default parameters or any destructured parameters. For example, in the following function that uses a default parameter, 10 instead of 100 is returned:

function bar(a=1) {
  arguments[0] = 100;
  return a;
}
bar(10); // 10

Specifications

Specification	Status	Comment
{{SpecName('ES1')}}	{{Spec2('ES1')}}	Initial definition. Implemented in JavaScript 1.1
{{SpecName('ES5.1', '#sec-10.6', 'Arguments Object')}}	{{Spec2('ES5.1')}}
{{SpecName('ES6', '#sec-arguments-exotic-objects', 'Arguments Exotic Objects')}}	{{Spec2('ES6')}}

Browser compatibility

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari
Basic support	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}

Feature	Android	Chrome for Android	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}	{{CompatVersionUnknown}}