`this` in callback functions

Question

I used to use

MyClass.prototype.myMethod1 = function(value) {
    this._current = this.getValue("key", function(value2){
        return value2;
    });
};

How do I access the value of this within the callback function like below?

MyClass.prototype.myMethod1 = function(value) {
   this.getValue("key", function(value2){
       //ooopss! this is not the same here!    
       this._current = value2;
   });
};

you could always pass `this` over as a second argument. Not sure if it would work though. — starbeamrainbowlabs, Jan 28 '13 at 12:12
It really does not have anything to do with whether a function is anonymous or not. — Felix Kling, Jan 28 '13 at 12:17

score 3 · Accepted Answer · answered Jan 28 '13 at 12:12

MyClass.prototype.myMethod1 = function(value) {
    var that = this;
    this.getValue("key", function(value2){
         //ooopss! this is not the same here!
         // but that is what you want
         that._current = value2;
    });

};

Or you could make your getValue method execute the callback with this set to the instance (using call/apply).

score 2 · Answer 2 · answered Jan 28 '13 at 12:12

2

Declare a variable in the external scope to hold your this :

MyClass.prototype.myMethod1 = function(value) {
    var that = this;
    this.getValue("key", function(value2){
         that._current = value2;
    });

};

answered Jan 28 '13 at 12:12

Denys Séguret

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score 1 · Answer 3 · answered Jan 28 '13 at 12:12

1

Declare it as a variable before

MyClass.prototype.myMethod1 = function(value) {
var oldThis = this;
 this.getValue("key", function(value2){
    /// oldThis is accessible here.
    });

};

answered Jan 28 '13 at 12:12

Dave Hogan

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`this` in callback functions

3 Answers3

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