Function (Built-in Object)
Function (內置對象)
Function is the object from which JavaScript functions are derived. Functions are first-class data types in JavaScript, so they may be assigned to variables and passed to functions as you would any other piece of data. Functions are, of course, reference types.
The Function object provides both static properties like length and properties that convey useful information during the execution of the function, for example, the arguments[] array.
Constructor
var instanceName = new Function([arg1 [, arg2 [, ...]] ,] body);
The body parameter is a string containing the text that makes up the body of the function. The optional argN's are the names of the formal parameters the function accepts. For example:
var myAdd = new Function("x", "y", "return x + y");
var sum = myAdd(17, 34);
Properties
arguments[] An implicitly filled and implicitly available (directly usable as "arguments" from within the function) array of parameters that were passed to the function. This value is null if the function is not currently executing. (IE4+ (JScript 2.0+), MOZ, N3+ (JavaScript 1.1+), ECMA Edition 1)
arguments.callee Reference to the current function. This property is deprecated. (N4+, MOZ, IE5.5+)
arguments.caller Reference to the function that invoked the current function. This property is deprecated. (N3, IE4+)
arguments.length The number of arguments that were passed to the function. (IE4+ (JScript 2.0+), MOZ, N3+ (JavaScript 1.1+), ECMA Edition 1)
arity Numeric value indicating how many arguments the function expects. This property is deprecated. (N4+, MOZ)
caller Reference to the function that invoked the current function or null if called from the global context. (IE4+ (JScript 2.0+), MOZ, N3+)
constructor Reference to the constructor object that created the object. (IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), ECMA Edition 1)
length The number of arguments the function expects to be passed. (IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), ECMA Edition 1)
prototype Reference to the object's prototype. (IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), ECMA Edition 1)
Methods
apply(thisArg [, argArray]) Invokes the function with the object referenced by thisArg as its context (so references to this in the function reference thisArg). The optional parameter argArray contains the list of parameters to pass to the function as it is invoked. (IE5.5+ (JScript 5.5+), N4.06+ (JavaScript 1.3+), MOZ, ECMA Edition 3)
call(thisArg [, arg1 [, arg2 [, ...]]]) Invokes the function with the object referenced by thisArg as its context (so references to this in the function reference thisArg). The optional parameters argN are passed to the function as it is invoked. (IE5.5+ (JScript 5.5+), N4.06+ (JavaScript 1.3+), MOZ, ECMA Edition 3)
toString() Returns the string version of the function source. The body of built-in and browser objects will typically be represented by the value "[native code]". (IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), MOZ, ECMA Edition 1)
valueOf() Returns the string version of the function source. The body of built-in and browser objects will typically be represented by the value "[native code]". (IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), MOZ, ECMA Edition 1)
Support
Supported in IE4+ (JScript 2.0+), N3+ (JavaScript 1.1+), MOZ, ECMAScript Edition 1.
Notes
General examples of functions are found throughout the book, but see Chapter 5 for examples of the advanced aspects of functions and the Function object.