Understand the caller,callee,call,apply of JavaScript

The article is very good, although I use jquery, but the feeling is still some use ~ ~ ~

First of all, I want to talk about the implicit parameters of functions in javascript: arguments

Arguments

The object represents the function being executed and the parameters of the function that called it.

[function.] Arguments[n]m.hrbfc120.com

Parameter function: option. The name of the Function object that is currently executing. N: Option. The 0-based parameter value index to pass to the Function object.

Description

Arguments is a hidden object that is created in addition to the specified arguments when a function call is made. Arguments is an array-like but not an array object, saying that it resembles an array because it has an array of access properties and methods, which can be accessed by arguments[n] to access the value of the corresponding single parameter and has the length property of the array. Also, the arguments object stores the arguments that are actually passed to the function, not limited to the list of arguments defined by the function declaration, and the arguments object cannot be created explicitly. The arguments object is available only when the function starts. The following examples illustrate these properties in detail:

The usage of the arguments object.

function Argtest (A, b) {

var i, S = "The Argtest function expected";

var Numargs = arguments.length; Gets the numeric value of the passed parameter.

var Expargs = argtest.length; Gets the numeric value of the desired parameter.

if (Expargs < 2)

s + = Expargs + "argument.";

Else

s + = Expargs + "arguments.";

if (Numargs < 2)

s + = Numargs + "was passed.";

Else

s + = Numargs + "were passed.";

s + = "\ n"

for (i =0; i < Numargs; i++) {//Get parameter contents.

s + = "Arg" + i + "=" + arguments[i] + "\ n";

}

return (s); Returns a list of parameters.

}

Here you add a code that illustrates that arguments is not an array class:

Array.prototype.selfvalue = 1;

Alert (new Array (). Selfvalue);

function testaguments () {

alert (Arguments.selfvalue);

}

Running the code you will find that the first alert shows 1, which means that the array object has the Selfvalue property, the value is 1, and when you call the function testaguments, you will find that "undefined" is displayed, indicating that the property is not arguments. That is, arguments is not an array object.

Caller

Returns a reference to the function that called the current function. M.mlyrx120.com

Functionname.caller

The FunctionName object is the name of the function being executed.

Description

For a function, the caller property is defined only when the function executes. If the function is called by the top level, then caller contains null. If you use the Caller property in a string context, the result is the same as functionname.tostring, that is, the deserialized text of the function is displayed.

The following example illustrates the use of the caller property:

Caller Demo {

function Callerdemo () {

if (Callerdemo.caller) {

var a= callerDemo.caller.toString ();

alert (a);

} else {

Alert ("This is a top function");

}

}

function Handlecaller () {

Callerdemo ();

}

Callee

Returns the function object being executed, which is the body of the specified function object.

[function.] Arguments.callee

The optional function parameter is the name of the function object that is currently executing.

Description

The initial value of the Callee property is the Function object that is being executed.

The Callee property is a member of the arguments object that represents a reference to the function object itself, which facilitates anonymous

recursive function or guarantee the encapsulation of functions, such as the following example of the recursive calculation of 1 to n the sum of natural numbers. And this property

Available only if the related function is executing. It is also important to note that Callee has the length property, which is sometimes

For validation or better. Arguments.length is the argument length, Arguments.callee.length is

Parameter length, which can be used to determine if the parameter length is the same as the argument length at the time of the call. M.120hrb.com

Example

Callee can print its own

function Calleedemo () {

alert (Arguments.callee);

}

Used to validate parameters

function Calleelengthdemo (arg1, arg2) {

if (arguments.length==arguments.callee.length) {

Window.alert ("Verify formal parameters and argument lengths are correct!");

Return

} else {

Alert ("Argument length:" +arguments.length);

Alert ("Parameter length:" +arguments.callee.length);

}

}

Recursive calculation

var sum = function (n) {

if (n <= 0)

return 1;

Else

return n +arguments.callee (n-1)

}

Comparison of general recursive functions:

var sum = function (n) {

if (1==n) return 1;

else return n + sum (n-1);

When invoked: Alert (SUM (100));

Where the function contains a reference to the sum itself, the function name is just a variable name, and calling sum inside the function is equivalent to calling

A global variable, not a good representation of the call itself, when using callee will be a better method.

Apply and call

Their role is to bind the function to another object to run, and the two differ only in the way that the parameter is defined:

Apply (Thisarg,argarray);

Call (Thisarg[,arg1,arg2 ...]);

That is, the this pointer inside all functions is assigned a value of Thisarg, which enables the purpose of running a function as a method of another object

Description of Apply

If Argarray is not a valid array or is not a arguments object, it will result in a TypeError.

If none of the Argarray and Thisarg parameters are provided, then the Global object will be used as a thisarg,

and cannot be passed any parameters.

Description of Call

The call method can change the object context of a function from the initial context to a new object specified by Thisarg.

If the Thisarg parameter is not provided, then the Global object is used as the Thisarg

Related tips:

There is also a technique for applying call and apply, in which another function (class) is applied with call and apply, and the current

A function (class) has a method or property of another function (class), which can also be called "Inheritance". Look at the following example:

Inherited demos

function Base () {

This.member = "Dnnsun_member";

This.method = function () {

Window.alert (This.member);

}

}

function Extend () {

Base.call (this);

Window.alert (member);

Window.alert (This.method);

}

As can be seen from the above example, extend can inherit the methods and properties of base after call.

By the way, using apply in the JavaScript framework prototype creates a schema that defines the class.

The implementation code is as follows:

var Class = {

Create:function () {

return function () {

This.initialize.apply (this, arguments);

}

}

}

Parsing: From the code perspective, the object contains only one method: Create, which returns a function, the class. But it's also a class.

constructor, which calls initialize, which is the initialization function defined at the time the class is created. Through this way,

You can implement the class creation pattern in prototype

Example:

var vehicle=class.create ();

vehicle.prototype={

Initialize:function (type) {

This.type=type;

}

Showself:function () {

Alert ("This vehicle is" + this.type);

}

}

var moto=new vehicle ("moto"); 3g.mlybyby.com

Moto.showself ();

Understand the caller,callee,call,apply of JavaScript