Javascript “this” keyword

The “this” keyword is an indispensable, yet often mis-understood, concept in JavaScript object-oriented programming. When used in a JavaScript constructor function, “this” refers to the specific instance of the Object. Through the “this” keyword, properties and methods can be assigned object, also known as a class.

For example:

function Square(intSideLength)
this.sideLength = intSideLength;

In the preceding example the “this” keyword is used to assign the variable “sideLength” as a property of the Square class.
The “this” keyword is also frequently passed as a parameter on JavaScript events, such as when a checkbox is clicked. In such an instance, “this” refers to the current object, the checkbox.


Eclipse FileSync plugin

I’ve done a lot of front-end java coding over my career,  one particularly annoying aspect is the wait for a build (compile-deploy) cycle in my local developement servers to view or test a small change.  One particularly useful tool that I’ve been using for some time is a FileSync plugin for Eclipse.  It is useful as you can “map” folders from your Eclipse project to a path on your local filesystem, as such the individual files are automatically copied to your server installation.  I’ve personally used this approache with JBoss, Tomcat and WebSphere, but there is no reason that it should not work for other servers.

JQuery equivalent to Element.identify(el)

Migrating between various javascript frameworks can often prove difficult, especially when developers become comfortable with the specific features of one library. Here is a feature that I’ve seen used in PrototypeJS that does not exist in jQuery, but can easily be added with a new function.

PrototypeJS provides an identify(el);function … Element.identify(el);. This is powerful in the sense that it returns the ‘id’ of an element, or automatically generates and assigns one when it is empty.

For jQuery the following can be added to emulate the functionality.

jQuery.fn.identify = function(prefix) {
var i = 0;
return this.each(function() {
if($(this).attr('id')) return;
do {
var id = prefix + '_' + i;
} while(document.getElementById(id) != null);
$(this).attr('id', id);

(function($) {// Compliant with jquery.noConflict()

X-XSS-Protection HTTP Header

This HTTP Header is a feature added by MSIE8 to force it to restrict some XSS vectors that can be disabled by the user. Generally you can add it into your webserver configuration.

X-XSS-Protection: 1; mode=block


JavaScript “use strict”

ECMAScript 5 added Strict Mode to JavaScript. Many of you may have first seen mention of this if you’ve used JSLint. It helps to remember that JavaScript still behaves much like an interpreted vs. compiled language as each browser/parser makes assumptions to execute code faster in different manners.

There are four primary features/goals of strict mode:

  • Throws errors for some common coding issues, that are sometimes obscure but previously didn’t throw an error.
  • Prevents or throws errors for potentially “unsafe” actions (such as gaining access to the global object).
  • Disables functions that are confusing or poorly thought out
  • Potentially code in strict mode could run faster by eliminating mistakes that would make it difficult for JavaScript engines to perform optimizations

Initial support added in FireFox 4 and MSIE10:

WARNING: if you chose to do this at a ‘file’ level, be sure to never concatenate several files together that are not ALL strict.

JS File Example:
"use strict";
function testFunction(){
var testvar = 1;
return testvar;

// This causes a syntax error.
testvar = 2;

JS Function Example:
function testFunction(){
"use strict";
// This causes a syntax error.
testvar = 1;
return testvar;
testvar = 2;


Browser performance impact of charset/codepage assignment

Most developers (myself included) are often unaware of the performance impact of the Content-Type / charset of a web page. Ideally you should set this as an HTTP Header vs. using META http-equiv. It’s often though that this only helps with the transport and display of data, however, the browser also makes use of it when parsing CSS & JS assets. Tags related to those provide an optional ‘charset‘ attribute should they ever need to vary from your content.

General guidance is to set this at the very top of the <head> before <title>; and within the first 1024 bytes, though there are reports that Firefox will look at the first 2048 bytes of the page for this META information.

Not doing so may cause the browser to do a codepage restart to re-parse assets that were interpreted in the potentially incorrect codepage.

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />


Prevent Firefox browser auto update

Often you find a neeed to keep an old copy of Firefox around for testing or to use a specific plugin (Example: Selenium). In these cases it can often prove problematic to allow the browser to auto-update. Here are some simple steps to prevent this behavior.

Enter “about:config” into the Firefox URL bar, then change the following values. You can click on them to toggle. = false
app.update.enabled = false

Alternately, on Windows you can edit the config file at: %APPDATA%\Mozilla\Firefox\Profiles\.default\prefs.js


No JavaScript support

There are still a measurable number of internet users that browse without the use of JavaScript, use the NoScript plugin, or have disabled it for security purposes. In those cases, as well as for SEO. It’s often a good idea to manipulate the display to better accomodate these users. One of the most common methods is shown below, as we can toggle a CSS class on the HTML tag easily and use CSS “cascade” to hide or show alternate content.

NOTE: this example currently requires PrototypeJS, but can easily be changed to not do so.

<!DOCTYPE html>
<html class="no-js">
<script type="text/javascript">
var ar = document.getElementsByTagName('html');
var i = ar.length;// should only be one!
<style type="text/css>
html .no-js-show { display:none; } .no-js-show { display:block; } .no-js-hide { display:none; }
JavaScript is:
<p class="no-js-hide">enabled</p>
<p class="no-js-show">JavaScript is disabled</p>

Browser Performance/Capability Benchmark Testing

In the past few years the browser wars have heated up again. Performance and capabilities of some browsers varies greatly. There are several standard tests that are publicly available to benchmark your systems. WebKit (Safari, Chrome & Chromium) and Mozilla (Firefox) based browsers, as well as Opera perform pretty well, MSIE is currently trailing in most cases.

Here are a few common ones…

JavaScript language attribute

Occasionally I’ve stumbled upon legacy javascript code that is used to determine javascript support by the visiting users. This often proves comical, because they are many times wasting time making checks for some “VERY OLD” browsers indeed! Here’s a rundown of the versions of javascript as well as their release dates and some common browser versions that implemented them.

  • JavaScript 1.0 (March 1996) = Navigator 2.0 / MSIE 3.0
  • JavaScript 1.1 (August 1996) = Navigator 3.0
  • JavaScript 1.2 (June 1997) = Navigator 4.0-4.05
  • JavaScript 1.3 (October 1998) = Navigator 4.06-4.7x / MSIE 4.0
  • JavaScript 1.4 = Netscape Server
  • JavaScript 1.5 (November 2000) = Navigator 6.0 / Firefox 1.0 / MSIE 5.5 – 8.0 / Safari 3.0-5 / Chrome 1.0-10.x / Opera 6.0
  • JavaScript 1.6 (November 2005) = Firefox 1.5
  • JavaScript 1.7 (October 2006) = Firefox 2.0
  • JavaScript 1.8 (June 2008) = Firefox 3.0 / Opera 11.50
  • JavaScript 1.8.1 = Firefox 3.5
  • JavaScript 1.8.2 (June 2009) = Firefox 3.6
  • JavaScript 1.8.5 (July 2010) = Firefox 4.0 / MSIE 9.0 / Opera 11.60

The language attribute has long been deprecated and should generally be avoided, it’s original purpose was to support other scripting languages, notably VBScript, or particular JavaScript versions. Modern conventions rely on specifying the MIME type instead via the ‘type’ attribute.

<SCRIPT LANGUAGE="JavaScript"> is now <script type="text/javascript">

<SCRIPT LANGUAGE="JavaScript1.1"> is now <script type="text/javascript1.1">

<SCRIPT LANGUAGE="VBScript"> is now <script type="text/vbscript">

<SCRIPT LANGUAGE="TCL"> is now <script type="text/tcl">