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Thread: Issue with function in prototype class

  1. #1
    Join Date
    Jan 2010
    Posts
    5

    Question Issue with function in prototype class

    Hi all,
    I'm trying to build a class this way:

    Code:
    function MouseLogger() {
    	this.fps = 2;
    	this.state = 0; //0 = stop, 1 = play, 2 = record
    	// recorded coordinates
    	this.eventsQueue = new Array(); 
            ...
    }
    I defined a function:

    Code:
    MouseLogger.prototype.init = function() {
    	log.debug("MouseLogger init");
    	this.startRecord();
    }
    which works when I call "this.init();" anywhere in the class.

    I did the same thing defining:

    Code:
    MouseLogger.prototype.addGuiEvent = function(e) {
    	if (e){
    		this.eventsQueue.push(e);
    		//log.debug("queue size: ",this.eventsQueue.size());
    	} else {
    		log.error("addEvent null");
    	}
    }
    But when I call "this.addGuiEvent(e);" my Firefox says:

    Code:
    Error: this.addGuiEvent is not a function
    I can't see anything wrong with it. Any hints?

    Thanks!
    Mulone

  2. #2
    Join Date
    Jan 2008
    Posts
    273
    I think I know what your problem is, and if thats it, you're not showing us enough code, so I'm guessing here.

    So, you probably do something like:
    Code:
    var obj = new MouseLogger() ;
    obj.addGuiEvent() ; 
    MouseLogger.prototype.addGuiEvent = function(e) { ... }
    right. Which doesn't work, but if you change it too:
    Code:
    MouseLogger.prototype.addGuiEvent = function(e) { ... }
    var obj = new MouseLogger() ;
    obj.addGuiEvent() ;
    it works!
    You have to make sure that the 'addGuiEvent' is defined at the moment you want to use it

    cheers

  3. #3
    Join Date
    Jan 2010
    Posts
    5
    Thanks for your answer!
    Actually I'm calling this function from another function:

    Code:
    MouseLogger.prototype.addGuiEvent = function(e) {
    	if (e){
    		this.eventsQueue.push(e);
    		//log.debug("queue size: ",this.eventsQueue.size());
    	} else {
    		log.error("addEvent null");
    	}
    }
    
    /**
    * fetch coordinates from current mouse event
    */
    MouseLogger.prototype.grabEvents = function(e) {
       if (!e) e = window.event;
       if (!e) log.error("grabCoordinates null event",e);
       
       if (e.pageX || e.pageY)
       {
           this.posx = e.pageX;
           this.posy = e.pageY;
       }
       else if (e.clientX || e.clientY){
           this.posx = e.clientX + document.body.scrollLeft;
           this.posy = e.clientY + document.body.scrollTop;
       }
       //log.debug("grabCoordinates",this.posx,this.posy)
       if (!this.posx || !this.posy){
    	   log.warn("grabCoordinates null coords");
           this.posx = null;
           this.posy = null;
       }
       log.error(this);
       this.addGuiEvent(e);
    }
    The function grabEvents is called here:

    Code:
    /**
    * start recording
    */
    MouseLogger.prototype.startRecord = function() {
      
       log.debug("MouseLogger startRecord");
       this.state = 1
       window.onmousemove = this.grabEvents;
    }
    I'm wandering if the onmousemove is related to this issue... Maybe the scope of "this" is different in this case.
    Any hints?

  4. #4
    Join Date
    Jul 2008
    Location
    urbana, il
    Posts
    2,787
    events have a different this than OOP methods.
    use "that" instead:

    Code:
    */
    MouseLogger.prototype.grabEvents = function me(e) {
      var that=me.that;
       if (!e) e = window.event;
       if (!e) log.error("grabCoordinates null event",e);
       
       if (e.pageX || e.pageY)
       {
           that.posx = e.pageX;
           that.posy = e.pageY;
       }
       else if (e.clientX || e.clientY){
           that.posx = e.clientX + document.body.scrollLeft;
           that.posy = e.clientY + document.body.scrollTop;
       }
       //log.debug("grabCoordinates",this.posx,this.posy)
       if (!that.posx || !that.posy){
    	   log.warn("grabCoordinates null coords");
           that.posx = null;
           that.posy = null;
       }
       log.error(that);
       that.addGuiEvent(e);
    }
    
    
    MouseLogger.prototype.startRecord = function() {
       MouseLogger.prototype.grabEvents.that=this;
       log.debug("MouseLogger startRecord");
       this.state = 1
       window.onmousemove = this.grabEvents;
    }
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  5. #5
    Join Date
    Jan 2010
    Posts
    5
    Thanks for your answer!
    Actually the "that" solution seems a bit akward... What's the proper way of handling this?
    I wanted to create a class containing all the logic I need, but maybe in JS I don't really need that.

    Mulone

  6. #6
    Join Date
    Jul 2008
    Location
    urbana, il
    Posts
    2,787
    Quote Originally Posted by Mulone View Post
    Thanks for your answer!
    Actually the "that" solution seems a bit akward... What's the proper way of handling this?
    I wanted to create a class containing all the logic I need, but maybe in JS I don't really need that.

    Mulone
    there isn't a perfect way. there is only one word, "this", that javascript uses for OOP and events; you have to dupe/shadow one of them when both are needed.


    you can use closure to cleanup the interface and avoid the extra that property, at a slight cost to speed:

    Code:
    MouseLogger.prototype.grabEvents = (function(){
      var that=this;
       return function(e) {
       if (!e) e = window.event;
       if (!e) log.error("grabCoordinates null event",e);
       
       if (e.pageX || e.pageY)
       {
           that.posx = e.pageX;
           that.posy = e.pageY;
       }
       else if (e.clientX || e.clientY){
           that.posx = e.clientX + document.body.scrollLeft;
           that.posy = e.clientY + document.body.scrollTop;
       }
       //log.debug("grabCoordinates",this.posx,this.posy)
       if (!that.posx || !that.posy){
    	   log.warn("grabCoordinates null coords");
           that.posx = null;
           that.posy = null;
       }
       log.error(that);
       that.addGuiEvent(e);
    }
    }());//end scope wrapper
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  7. #7
    Join Date
    Feb 2003
    Location
    Michigan, USA
    Posts
    5,774
    If you want, you can wrap up the function closure solution into something reusable:

    Code:
    function getFunctionInContext( context, fn ) {
    	return function() {
    		return fn.apply( context, arguments );
    	};
    }
    Then to use:

    Code:
    window.onmousemove = getFunctionInContext( this, this.grabEvents );
    Then the "this" keyword inside grabEvents will point to the instance of the MouseLogger class instead of the window object.

  8. #8
    Join Date
    Dec 2003
    Location
    Bucharest, ROMANIA
    Posts
    15,428
    Quote Originally Posted by toicontien View Post

    Code:
    window.onmousemove = getFunctionInContext( this, this.grabEvents );
    I used to think that window object supports only few events (onload, onblur, onfocus, onerror, onunload and onbeforeunload [non standard]). I would say that onmousemove should be attached to the document object
    Code:
    document.onmousemove= ...

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