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desperate on javascript issue


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#1 JohnnyCode   Members   -  Reputation: 273

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Posted 30 September 2012 - 07:10 PM

Hi,

I have implemented a 'class' in javascript like this
function CMesh()
{
	this.m_faVerticies=new Array();
	this.m_fWorld=new Array();
	this.m_fFile;
	CMesh.prototype.FeedAFile = function(uri) {
		// code

		var xmlhttp=new XMLHttpRequest();
		
		xmlhttp.onreadystatechange=function()
		  {
		  if (xmlhttp.readyState==4 && xmlhttp.status==200)
			{
				 var bytes = xmlhttp.responseBody;

				  this.m_fFile= bytes.toArray();
						this.m_faVerticies = new Array();
					  var n=0;
						for (var i = 0; i < this.m_fFile.length; i=i+4)
					   {
							 var fl=decodeFloat(i,this.m_fFile, 1, 8, 23, -126, 127, true);
							 this.m_faVerticies[n]=fl;
							 n++;
	 	 	 	 	 }
						alert( this.m_faVerticies.length+'A');// ALERTS CORRECT VALUE-9A
			}
		  }
		  xmlhttp.open("GET",uri,false);

		xmlhttp.send();

	}
}
If I call this function - FeedAFile, on an instance, I get from my debug alert "9A", which is correct.
but If I read the member m_faVerticies on a next alert(), all hapyness is gone
mesh=new CMesh();
		mesh.FeedAFile('onefloat.bin');// THE FUNCTION ALERTS '9A'
		alert(mesh.m_faVerticies.length); // THIS FOLLOWING ALERT OUTPUTS 0
I have no idea as where the member .m_faVerticies changed. Have I implemented the class with a public variable incorrectly?

Thanks in advance

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#2 wqking   Members   -  Reputation: 756

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Posted 30 September 2012 - 08:07 PM

I'm not a JS guru.
I can only guess that you assign m_faVerticies to a wrong object than mesh.
Can you alert value "this" inside of FeedAFile and value "mesh" outside of FeedAFile?

http://www.cpgf.org/
cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.
v1.5.5 was released. Now supports tween and timeline for ease animation.


#3 JohnnyCode   Members   -  Reputation: 273

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Posted 30 September 2012 - 08:32 PM

Can you alert value "this" inside of FeedAFile and value "mesh" outside of FeedAFile?

Thanks , but this will alert only the object type, not something like poiner value or so

#4 wqking   Members   -  Reputation: 756

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Posted 01 October 2012 - 12:31 AM

I tested your code (cut down version) and seems m_faVerticies is assigned to correct object.
So there must be some other reasons.

http://www.cpgf.org/
cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.
v1.5.5 was released. Now supports tween and timeline for ease animation.


#5 JohnnyCode   Members   -  Reputation: 273

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Posted 01 October 2012 - 05:28 AM

thanks very much. .... interesting
was it alerting 0 or more? Also I did'nt provide defintion for decodeFloat(i,this.m_fFile, 1, 8, 23, -126, 127, true); so then you perhaps defined it to return just constant float. (I am not on a PC with source right now, cannot post the definition, but I think I will work around and test the code by altering it, I will try add floats to array by hand and so on)
I was on Win 7 64bit, ie 9. What browser and OS have you got? Thank you for your effort, I hope you find this code usefull.

#6 wqking   Members   -  Reputation: 756

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Posted 01 October 2012 - 05:55 AM

I have to comment out some code to make it run.
The two alerts are "3A" and "3", so they are correct.
I tested on WinXP, in both IE 8 and FireFox 12.
[source lang="xml"]<html><head></head><body><script>function CMesh(){ this.m_faVerticies=new Array(); this.m_fWorld=new Array(); this.m_fFile; CMesh.prototype.FeedAFile = function(uri) { // code// var xmlhttp=new XMLHttpRequest(); // xmlhttp.onreadystatechange=function() { if (1) {// var bytes = xmlhttp.responseBody;// this.m_fFile= bytes.toArray(); this.m_faVerticies = new Array(); var n=0; for (var i = 0; i < 9; i=i+4) { var fl=1; this.m_faVerticies[n]=fl; n++; } alert( this.m_faVerticies.length+'A');// ALERTS CORRECT VALUE-9A } }// xmlhttp.open("GET",uri,false);// xmlhttp.send(); }}mesh=new CMesh();mesh.FeedAFile('onefloat.bin');alert(mesh.m_faVerticies.length);</script></body></html>[/source]

Edited by wqking, 01 October 2012 - 05:56 AM.

http://www.cpgf.org/
cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.
v1.5.5 was released. Now supports tween and timeline for ease animation.


#7 gretty   Members   -  Reputation: 212

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Posted 03 October 2012 - 04:46 AM

Maybe try to place the public function FeedAFile() outside the class definition. Not sure if this will make any difference, I've always placed the public functions outside the class definition. Functions inside the class defintion(that are not prototype) are still public from what I remember but they can also access and change private variables.

function CMesh()
{
		this.m_faVerticies=new Array();
		this.m_fWorld=new Array();
		this.m_fFile;
	  
		var privateVar = 1;
		// This maybe incorrect but I think ONLY the following
		// type of functions can be inside the class declaration
		this.MyFunction = function(foo) {
			   // access and change private and public variables
		}
}

CMesh.prototype.FeedAFile = function(uri) {
				// code
				var xmlhttp=new XMLHttpRequest();
			  
				xmlhttp.onreadystatechange=function()
				  {
				  if (xmlhttp.readyState==4 && xmlhttp.status==200)
						{
								 var bytes = xmlhttp.responseBody;
								  this.m_fFile= bytes.toArray();
												this.m_faVerticies = new Array();
										  var n=0;
												for (var i = 0; i < this.m_fFile.length; i=i+4)
										   {
														 var fl=decodeFloat(i,this.m_fFile, 1, 8, 23, -126, 127, true);
														 this.m_faVerticies[n]=fl;
														 n++;
										 }
												alert( this.m_faVerticies.length+'A');// ALERTS CORRECT VALUE-9A
						}
				  }
				  xmlhttp.open("GET",uri,false);
				xmlhttp.send();
}

Edited by gretty, 03 October 2012 - 04:47 AM.


#8 tanzanite7   Members   -  Reputation: 1363

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Posted 03 October 2012 - 01:53 PM

This code looks very fishy ...

function CMesh() {
	this.m_faVerticies=new Array();
	// etc

	CMesh.prototype.FeedAFile = function(uri) {
		var xmlhttp=new XMLHttpRequest();
		xmlhttp.onreadystatechange=function() { // lambda function
			 // cut
			 this.m_fFile= bytes.toArray();
			 // cut
		}
	}
}

1. take CMesh.prototype.FeedAFile out of the class "constructor". You are needlessly reassigning the prototype function with every new object - it is unnecessary. Every new object will inherit the same function from the prototype chain anyway - that is what prototype is for.
2. "this.m_fFile" in the lambda function will point to the lambda function itself - which does not have any of the CMesh properties (edit: ie, all of the data will be thrown away the moment "FeedAFile" function ends).

Something like:
function CMesh() {
	this.m_faVerticies=new Array();
	// etc
}
CMesh.prototype.FeedAFile = function(uri) {
	var xmlhttp=new XMLHttpRequest();
	var that = this; // because closure is fun - aka, we want to give the lambda function access to "this" of the CMesh object.
	xmlhttp.onreadystatechange=function() { // lambda function
		 // cut
		 that.m_fFile= bytes.toArray(); // notice "that" instead of "this".
		 // cut
	}
}

Edited by tanzanite7, 03 October 2012 - 02:02 PM.


#9 wqking   Members   -  Reputation: 756

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Posted 04 October 2012 - 04:38 AM

2. "this.m_fFile" in the lambda function will point to the lambda function itself - which does not have any of the CMesh properties (edit: ie, all of the data will be thrown away the moment "FeedAFile" function ends).

Something like:

function CMesh() {
	this.m_faVerticies=new Array();
	// etc
}
CMesh.prototype.FeedAFile = function(uri) {
	var xmlhttp=new XMLHttpRequest();
	var that = this; // because closure is fun - aka, we want to give the lambda function access to "this" of the CMesh object.
	xmlhttp.onreadystatechange=function() { // lambda function
		 // cut
		 that.m_fFile= bytes.toArray(); // notice "that" instead of "this".
		 // cut
	}
}

Very good spot.
Though I rarely used JS, I used Flash AS3 a lot which is quite JS like. In AS3 the "this" in a closure is also quite tricky.

http://www.cpgf.org/
cpgf library -- free C++ open source library for reflection, serialization, script binding, callbacks, and meta data for OpenGL Box2D, SFML and Irrlicht.
v1.5.5 was released. Now supports tween and timeline for ease animation.





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