javascript variable scope across functions jQuery involved

Question

Here is what i cannot get to work - in mouseMove this.mouseX is undefined. I need the mouseX and mouseY (e.pageX in code) from mousemove event.

function myClass () {
    var mouseX=x;
    var mouseY=y;
    $(document).mousemove(this.mouseMove);
}
myClass.prototype.mouseMove = function(e){
    this.mouseX=e.pageX;//not a good idea but you can alert this
}
var a=new myClass();

Can i get that event passed to the supposed class instance or there is no way to get it done?

I should also mention i am trying to avoid global scope variables here.

Felix Kling · Accepted Answer · 2011-06-25 13:55:57Z

1

~~Two~~ three things:

var mouseX only declares a variable local to the myClass function. You have to declare a property of the instance with this.mouseX (this refers to the current instance):

function myClass () {
    this.mouseX=x;  // where do x and y come from?
    this.mouseY=y;
    //...
}

Secondly, make sure you pass x and y as parameters to the constructor. Otherwise you will get an error (if they are not defined in higher scope, but that does not seem useful to me).

Thirdly, if you just pass this.mouseMove as event handler, inside the event handler, this will refer to window and not to the myClass instance. Use $.proxy to set the context of the callback explicitly:

function myClass(x, y) {
    this.mouseX=x;
    this.mouseY=y;
    $(document).mousemove($.proxy(this.mouseMove, this));
}

I suggest to read MDC - Working with objects.

edited Jun 25, 2011 at 13:55

answered Jun 25, 2011 at 13:49

Felix Kling

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1 Comment

Martin Over a year ago

first two things are just mistakes in my copy-paste-erase example making process, third one is what i was looking for, ty :D

nrabinowitz · Accepted Answer · 2011-06-25 13:51:25Z

0

When you pass a method like this.mouseMove as a callback function, it's no longer tied to the instance - so this will be the global object. To fix the scope, you can pass the instance in a closure, like so:

function myClass (x,y) {
    var mouseX=x;
    var mouseY=y;
    var that = this;
    $(document).mousemove(function() { that.mouseMove() });
}

answered Jun 25, 2011 at 13:51

nrabinowitz

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Comments

Mike · Accepted Answer · 2011-06-25 13:51:51Z

0

Try:

function myClass (x,y) {
    var mouseX=x;
    var mouseY=y;
    var $this = this;

    $(document).mousemove(function(){$this.mouseMove()});
}
myClass.prototype.mouseMove = function(e){
    this.mouseX=e.pageX;//not a good idea but you can alert this
}
var a=new myClass();

answered Jun 25, 2011 at 13:51

Mike

1

Comments

Kevin Bowersox · Accepted Answer · 2011-06-25 13:52:36Z

0

function myClass () {
    this.mouseX=x;
    this.mouseY=y;
    $(document).mousemove(this.mouseMove);
}
myClass.prototype.mouseMove = function(e){
    this.mouseX=e.pageX;//not a good idea but you can alert this
}
var a=new myClass();

You need to use the this keyword and not var to instantiate in the constructor

answered Jun 25, 2011 at 13:52

Kevin Bowersox

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