Using objects to correctly replace global variables

Question

I've been trying to figure out how to initialize an object using a prototype in order to escape using global variables, which I first learned about here. I began implementing my own version of the code found in the accepted answer.

function XML_Data() {
  this.data = null;
}

XML_Data.prototype = {
 GetXML: function() {
  $.ajax({
   type: "GET",
   url: "questions.xml",
   dataType: "xml",
   success: function(xml) {
    this.data=xml;
   } //close success
  });//close AJAX  
 },

 UseXML: function() {
  alert(this.data)
 }
};

(My implementation of the script)

However, I've run into a problem. When I run the functions shown here by using this bit of code:

var data = new XML_Data();
data.GetXML();
data.UseXML();

I get an alert that says "null". I've been through the code about a dozen times, but as this is my first time working with Javascript, there's quite obviously something I've missed. Could you point that out?

Thanks, Elliot Bonneville.

Do you want to use the Ajax data immediately? How often do you get new data via Ajax? — Šime Vidas
– Šime Vidas, Commented Nov 18, 2010 at 1:42

John Hartsock · Accepted Answer · 2010-11-18 01:50:37Z

2

Just of note

var data = new XML_Data();
data.GetXML();  //This will run the ajax request
data.UseXML();  //This will most likely run before the ajax request is finished.

Publishing events in Jquery would problably work,but I havent tested this code.

function XML_Data() {
  this.data = null;
}

XML_Data.prototype = {
 GetXML: function() {
  $.ajax({
   type: "GET",
      url: "questions.xml",
   dataType: "html",
   success: function(xml) {
    this.data=xml;
    $(window).trigger("myAjaxEvent");
   } //close success
  });//close AJAX  
 },

 UseXML: function() {
  alert(this.data)
 }
};


$(document).ready( function () {
    var data = new XML_Data();
    $(window).bind("myAjaxEvent", function () {
      data.UseXML();
    });

    data.GetXML();

});

edited Nov 18, 2010 at 1:50

answered Nov 18, 2010 at 1:26

John Hartsock

87.1k23 gold badges135 silver badges146 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Elliot Bonneville Over a year ago

Is that so? How would I fix that?

John Hartsock Over a year ago

@Elliot ... you could try publishing events using jquery

Zach · Accepted Answer · 2010-11-18 02:06:01Z

0

The code you have now is attempting to run synchronously (in order) using a non-blocking asynchronous API. The UseXML call happens before the GetXML call actually finishes doing its AJAX thing, because it's asynchronous.

You could write this in an asynchronous pattern (in which this.UseXML is called directly on success of the AJAX request), or a synchronous pattern (in which "async:false" is passed to the AJAX call). The asynchronous pattern is much more common in JavaScript development, as it is much more powerful, and synchronous requests block the UI in the browser by preventing script execution, but synchronous is much easier to do for little things.

See http://api.jquery.com/jQuery.ajax/

answered Nov 18, 2010 at 2:06

Zach

7,9503 gold badges24 silver badges26 bronze badges

Collectives™ on Stack Overflow

Using objects to correctly replace global variables

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related