IE6 and JavaScript performance
Published on 22nd June 2007 Estimated Reading Time: 2 minutesHaving been exposed to an application at work that uses a lot of JavaScript, I fully appreciate what some mean when they discuss IE6's inefficient handling of JavaScript. After seeing a web page taking an age to reload and your CPU taking a hammering because of JavaScript processing, the penny does tend to drop...
Needless to say, this very much impacts the world of AJAX-driven web applications with their heavy dependence on client-side JavaScript. While IE7 does come to the rescue, there remain plenty of IE6 users still out there, and this is reflected in website statistics. This demonstrates a certain level of inertia in the browser market that not only afflicts the uptake of IE7 but also the likes of Mozilla, Opera and Safari. It also means that anyone developing AJAX applications very much needs to continue testing in IE6, especially if the product of their labours is for wider public use.
An example of such an application is Zimbra, an open-source web application for messaging and collaboration, and the people behind it have generously shared the results of their browser performance benchmarking. They did comparisons of IE6 vs. IE7 and Firefox 2 vs. IE7. IE6 easily came out as the worst of these, while Firefox 2 was the best.
The next question to be asked could centre around the type of code that is processed inefficiently by IE6. While I wouldn't be at all surprised if a list emerged, here's one: using Microsoft's proprietary innerHTML object to update the DOM for a web page format. Having a quick trawl on Google, this came up for mention as a cause of memory leaks. It is also a Microsoft innovation that never got taken up by those overseeing web standards, hardly a surprise since a spot of DOM scripting achieves the same end. It may be faster to code than any alternatives, and it does have some support from other browsers, but it does seem to have got a bad name, so it should be avoided if possible. That said, it would be interesting to see a performance comparison between innerHTML and DOM methods in IE6.