The understanding of JavaScript this

has been to JS this does not understand, recently read the essence of the JavaScript language related chapters, a little clear understanding of the record

/* From: The essence of JavaScript language method: When a function is defined as a property of an object, we call it a method. This: When the function accesses this, the this is bound to the global object. *///global function var log = function (msg) {    Document.writeln ("<br>" + msg + "<br>");}; Log ("**************thistest.js***************");//define a global variable var value = 100;//function var add = function (A, b) {    var value = One by one;    Access internal variable    log ("Add:value =" + value);  Output Add:value = one    //When accessing this, the this binding global object, such as This.value, can access the value log defined above    ("Add:this.value =" + This.value); Outputs    A + b;} Add is a function that accesses this in add, and this binds to the global object Add (1, 2);//output://add:value = 11//add:this.value = 100

The following defines an object

Object var myObj = {    ///object property    value:0,    //Method    increment:function (inc) {//when        accessing this at this time, the MYOBJ object of this binding        log ("Myobj.increment (): Myobj.value =" + this.value);//output Myobj.value value        //Call value Increment 1        this.value + = typeof inc = = = ' number '? Inc:1;    }};

Sometimes we define a function inside a method, so how does the function call the object property, if the function content directly with this is not access to the object's

Object var myObj = {    ///object property    value:0,    //Method    increment:function (inc) {//when        accessing this at this time, the MYOBJ object of this binding        log ("Myobj.increment (): Myobj.value =" + this.value);//output Myobj.value value        //Call value Increment 1        this.value + = typeof inc = = = ' number '? Inc:1;        Defines an intrinsic function, or a function, so that the inside of the function accesses this or is only accessible to the global object        var infun = function () {            //At this time when accessing this, the this binding global object, such as This.value You can access the value log defined above            ("MyObj.increment.inFun:this.value =" + This.value);        };        Infun ();    }};

In order to access the MyObj object within the Infun function, we first save the MyObj object in a variable,

Object var myObj = {    ///object property    value:0,    //Method    increment:function (inc) {        ///To save the current object MYOBJ reference in the self variable, The subsequent function can access self to replace the Access MyObj object        var self = this;        At this time, when this is accessed, the this binds the MYOBJ object        log ("Myobj.increment (): Myobj.value =" + this.value);//output Myobj.value value        //Call once Value increased by 1        this.value + = typeof Inc = = = ' number '? Inc:1;        Defines an intrinsic function, or a function, so that the inside of the function accesses this or is only accessible to the global object        var infun = function () {            //At this time when accessing this, the this binding global object, such as This.value You can access the value log defined above            ("MyObj.increment.inFun:this.value =" + this.value);            log ("MyObj.increment.inFun:myObj.value =" + Self.value);        };        Infun ();    }};

Add a double method to MyObj

myobj.double = function () {    var = this;    var helper = function () {        //This can not be accessed with This.value to Myobj.value value        //add before the This may be omitted, or can be used This.add (A, b);        Self.value = Add (Self.value, self.value);    };    Helper ();};

Double the value of Myobj.value by calling the Double method

The understanding of JavaScript this