NS_ERROR_NOT_AVAILABLE: Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIDOMWindow.alert]

Sunday, December 23, 2012

This is a common error in Firefox. It is logged in console when you try to call on non existent DOM API method. Seeing this error message is very common with methods call to alert(), confirm(), drawImage() (canvas) and window.open(). You may think "how those methods could be 'non-existent'?", since they are standard APIs of the window object. Well, that's true, they can't, but consider the case when browser blocks your alert or pop-up windows. Firefox pop-up blocker will make those methods not available in that context and should silently carry on with the next statement, but instead it throws an error.

To solve this problem:

make sure you are calling methods on non-null objects;
remove alert(), confirm() or open() methods in unload event handler. FF pop-up blocker ignores all window.open() methods in the unload handler.

The flavours of the error message:

NS_ERROR_NOT_AVAILABLE: Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIDOMWindow.alert]
NS_ERROR_NOT_AVAILABLE: Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIDOMWindow.confirm]
NS_ERROR_NOT_AVAILABLE: Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIDOMCanvasRenderingContext2D.drawImage]

At the time of writing the problem has not been fixed.

Dynamically change <title> using jQuery

Monday, December 10, 2012

Tags: beginner, howto, jquery, manipulation

In this post I will show how to dynamically change document's title using JavaScript and jQuery. Browsing the web (and StackOverflow) I saw a lot of posts that say you can't do it using jQuery. Actually, there is a jQuery syntax that is basically a wrapper for javascript code (see below).

Note: just to clarify, by document title we mean the text that is displayed in the browser window or a tab.

The best way to change the document title is to use native javascript api document.title.

document.title = "New text set by JavasSript";

The equivalent jQuery code of js code above.

$(document).prop('title', 'New text set by jQuery');

Example

Let's say we need to change the tab title text when a user clicks on a button. Here is a jQuery code to do just that:

<html>
<head>
  <title>Initial page title</title>
  <script src="path-to/jquery.js"></script>
  <script>
    $(document).ready(function(){
      $('#clickme').click(function(){
        document.title = $(this).val();
        // jQuery syntax alternative
        // $("title").text( $(this).val() );
      });
    });
  </script>
</head>
<body>
  <input type="button" id="clickme" name="clickme" value="Click me!" />
</body>
</html>

To conclude, you are better off using document.title, because it is cross-browser and has performs better.

Alternative jQuery syntax has been tested in all major browsers.

The difference between == and === in jQuery/JavaScript

Friday, November 09, 2012

Tags: beginner, javascript, jquery, reference, tip

In this post I would like to explain the difference between double (==) and triple (===) equals in JavaScript/jQuery. A quick and short explanation is that == does type coercion (conversion) before checking for equality; and === does strict equation which requires values to have the same type as well.

Here is what it means:

0 == false     // true
0 === false    // false, because they have different types (int, bool)
1 == "1"       // true
1 === "1"      // false, because they have different types (int, string)
null == undefined // true
null === undefined // false

Detailed (longer) explanation

When you use == the javascript interpreter will convert one side of the comparison according to these rules:

When comparing a number and a string, the string is converted to a number value.
When comparing a boolean, the boolean is converted to 1 if it is true and +0 if it is false.
When object is compared with a number or a string, the object is converted to its’ default value (.valueOf(), .toString()). If these methods are missing a runtime error is thrown.
When comparing an object and another object, no type conversion is made. They are equal only if they refer the same object.

When you use === the javascript interpreter will not convert values to primitive types and make sure that the operands have the same value as well as the same type.

"foo" === "foo"  // true, both operands are of type String
new String("foo") === new String("foo")  // false, 2 Objects refer diff object instances

Detailed comparison information can be found on Mozilla Developer Network page. Here is the summary:

Two strings are strictly equal when they have the same sequence of characters, same length, and same characters in corresponding positions
Two numbers are strictly equal when they are numerically equal (have the same number value). NaN is not equal to anything, including NaN. Positive and negative zeros are equal to one another
Two Boolean operands are strictly equal if both are true or both are false
Two distinct objects are never equal for either strictly or abstract comparisons
An expression comparing Objects is only true if the operands reference the same Object
Null and Undefined Types are == (but not ===)

Add jQuery to your Greasemonkey script

Friday, August 05, 2011

Tags: howto, jquery, tip, workaround

Greasemonkey is a Firefox add-on that lets you run JavaScript on web pages you specify. Using Greasemonkey you can improve and change the way websites look and behave (see examples of what is possible here). To learn more about it see it's official site, to learn how to include and write your own custom scripts (aka "user scripts") visit coder's manual.

Usually Greasemonkey scripts work with the DOM and jQuery is the best way to do that. So, no wonder you'll want to include jQuery into your custom scripts. Here are 3 ways to include jQuery library into your user script.

If you are targeting for Greasemonkey 0.8.0+ you can use @require. It runs once when the script is being installed, hence downloaded once. This is preferred and most efficient way to add jQuery.

// ==UserScript==
// @name     My jQuery Test
// @require  http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js
// ==/UserScript==

// Do your magic here
$(".ads").remove();

If you are developing for older versions of Greasemonkey you have 2 options. Either add the whole jQuery library code into your Greasemonkey script file or dynamically add a <script> tag to the page.

Adding jQuery library right in your custom script

// ==UserScript==
// @name     My jQuery Test
// ==/UserScript==

// include jQuery library
/*!
 * jQuery JavaScript Library v1.6.2
 * http://jquery.com/
 *
 * Copyright 2011, John Resig
 * Dual licensed under the MIT or GPL Version 2 licenses.
 * http://jquery.org/license
 *
 * Includes Sizzle.js
 * http://sizzlejs.com/
 * Copyright 2011, The Dojo Foundation
 * Released under the MIT, BSD, and GPL Licenses.
 *
 * Date: Thu Jun 30 14:16:56 2011 -0400
 */
(function(a,b){function cv(a){return f.isWindow(a)? ...

One more method to add jQuery

One more way to add jQuery is by attaching <script> tag to the document. You can read more about it and grab the code here.

Don't forget to check if jQuery is already loaded

if (unsafeWindow.jQuery === undefined) {
  // jQuery is NOT loaded
} else {
  // jQuery is already loaded
}

HTML: The difference between attribute and property

Monday, June 13, 2011

Tags: attributes, beginner, DOM, html, insights, reference

In this short post I will explain the difference between attributes and properties in HTML. The .prop() function introduced in jQuery 1.6 raised a lot of questions about the difference and I hope this post will help you to understand it.

What is an attribute?

Attributes carry additional information about an HTML element and come in name=”value” pairs. Example: <div class=”my-class”></div>. Here we have a div tag and it has a class attribute with a value of my-class.

What is a property?

Property is a representation of an attribute in the HTML DOM tree. So the attribute in the example above would have a property named className with a value of my-class.

Our DIV node
 |- nodeName = "DIV"
 |- className = "my-class"
 |- style
   |- ...
 |- ...

What is the difference between attribute and property?

Attributes are in your HTML text document/file, whereas properties are in HTML DOM tree. This means that attributes do not change and always carry initial (default) values. However, HTML properties can change, for example when user checks a checkbox, inputs text to textarea or uses JavaScript to change the property value.

Here is a visual representation:

HTML                          DOM
<input value="default" />     value = default



----------------
Current values:
Attribute: "default"          Property:  "default"

Assume user inputs his name "Joe" into the inputbox. Here are what attribute and property values of an element will be.

HTML                          DOM
<input value="default" />     value = Joe



----------------
Current values:
Attribute: "default"          Property:  "Joe"

As you can see, only element’s property is changed, because it is in the DOM and dynamic. But element’s attribute is in HTML text and can not be changed!

I hope this helps to understand the difference between attributes and properties. If you have any questions please leave them on jQueryHowto Facebook page.

Also, stay tuned for the next post about the difference between jQuery.attr() and jQuery.prop() and when to use one over another.