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Problems with function literal used as DWR callback.

Posted on 2007-12-03
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Last Modified: 2008-02-27
I have written a piece of code to be executed on form submit. The code consists of a containing object called EventHandler which handles both initialisation and execution of event handlers.

I use prototype for the eventhandling code. The problem is that the property error of type StringBuffer (another object) does not play well with the function literal myCallback (which is invoked by DWR).

I want to store all validation errors in the error property for access later but neither of the two versions I have attached the code to does the trick for me. I am guessing it has to do with the scope in JavaScript but I can't pinpoint the problem.

Any help greatly appreciated!
//
//Invoked by
//
Event.observe(matchPlayerFormId, 'submit', this.formSubmit.bind(this));
 
//
//Version 1
//
EventHandler.prototype.formSubmit = function(event) {
	this.error = new StringBuffer();
 
	var myCallback = function(data){
		console.log("in callback, result = '" + data + "'");
		if (data.length > 0) {
			this.error.append(data);
			console.log("Intermediate: " + error.toString());
		}
	};
 
	for (var i = 0; i < this.validationNodes.length; i++){
		var variableId = this.validationNodes[i].id;
			
		var variableName = this.validationNodes[i].name;
	
		var variableValue = document.getElementById(variableId).value;
		
		JMatchValidator.validate(variableName, variableValue, myCallback.bind(this));
 
	}
		
	if (this.error.length() > 0){
		console.log("Submit cancelled");
		Event.stop(event);
		
	}
}
 
//
//Version 2
//
EventHandler.prototype.formSubmit = function(event) {
	var error = new StringBuffer();
 
	var myCallback = function(data){
		if (data.length > 0) {
			error.append(data);
		}
	};
 
	alert("Start submit");
	for (var i = 0; i < this.validationNodes.length; i++){
		var variableId = this.validationNodes[i].id;
			
		var variableName = this.validationNodes[i].name;
	
		var variableValue = document.getElementById(variableId).value;
 
		JMatchValidator.validate(variableName, variableValue, myCallback.bind(this));
 
	}
		
	if (error.length() > 0){
		console.log("Submit cancelled");
		Event.stop(event);
		
	}
}

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Question by:kveasana
4 Comments
 
LVL 29

Accepted Solution

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Badotz earned 500 total points
ID: 20524057
// Try this:
//
var self = this;
JMatchValidator.validate(variableName, variableValue, myCallback.bind(this, self));

// I have noticed that "bind" drops the first object from the argument list
// The first object bwcomes the object that is "called"
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Expert Comment

by:Computer101
ID: 20999905
Forced accept.

Computer101
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