Team LiB   Previous Section   Next Section
Arguments arguments and other properties of a function


JavaScript 1.1; JScript 2.0; ECMAScript v1

Inherits from/Overrides

Inherits from Object





The Arguments object is defined only within a function body. Although it is not technically an array, the Arguments object has numbered properties that function as array elements and a length property that specifies the number of array elements. Its elements are the values that were passed as arguments to the function. Element 0 is the first argument, element 1 is the second argument, and so on. All values passed as arguments become array elements of the Arguments object, whether or not those arguments are given names in the function declaration.



A reference to the function that is currently executing.


The number of arguments passed to the function and the number of array elements in the Arguments object.


When a function is invoked, an Arguments object is created for it and the local variable arguments is automatically initialized to refer to that Arguments object. The main purpose of the Arguments object is to provide a way to determine how many arguments were passed to the function and to refer to unnamed arguments. In addition to the array elements and length property, however, the callee property allows an unnamed function to refer to itself.

For most purposes, the Arguments object can be thought of as an array with the addition of the callee property. However, it is not an instance of Array, and the Arguments.length property does not have any of the special behaviors of the Array.length property and cannot be used to change the size of the array.

The Arguments object has one very unusual feature. When a function has named arguments, the array elements of the Arguments object are synonyms for the local variables that hold the function arguments. The Arguments object and the argument names provide two different ways of referring to the same variable. Changing the value of an argument with an argument name changes the value that is retrieved through the Arguments object, and changing the value of an argument through the Arguments object changes the value that is retrieved by the argument name.

See Also

Function; Chapter 7

    Team LiB   Previous Section   Next Section