JScript in Internet Explorer 8 Beta 1 for Developers

janakiram.msv — Wed, 05 Mar 2008 17:10:00 GMT

Making developers more productive through the design, development, and debug phases of web application development is one of the key goals for Internet Explorer 8. I’d like to take this opportunity to walk you through the features that the JScript team contributed to IE8 Beta 1 for Developers.

Let me start with the JScript language and the scripting engine optimization. Performance of the JScript engine has been our number one goal for the Beta1 release. With today’s rich AJAX web-applications, some of the most common JScript operations include String and Array operations. We received feedback from developers on the slow performance of the inbuilt string concatenation functions of JScript. This is not a new problem and quite a lot has been written about the issue (discussed in this Jscript blog post). With IE8, we fixed this problem in the JScript engine. String concatenation is now many times faster when compared to the previous JScript engine.

Prior to this optimization of string concatenation, most developers used Array join operations to achieve the same result. We were aware of this tradeoff and made sure that the Array operations are also optimized. In either scenario, developers will experience significant performance gains.

One of the challenges for the team was to understand the language compatibility and issues that existed in our JScript implementation of the ECMAScript Language Specification 3rd Edition. We have identified the JScript Deviations from ES3 (discussed in detail in this blog post). This document will act as a starting point for the developers targeting cross browser web applications and helps in understanding the deviations in detail. In the near future, we intend to make JScript more compatible with ES3 specifications.

Another challenge for the JScript developers is the circular memory leak problem. We took a hard look at this problem and realized that this has to be fixed at the COM infrastructure. We implemented a design that bridges the gap between COM ref-counting and automatic garbage collection models. We extended the IDispatchEx interface to enable COM clients to simultaneously live in both the ref-counted and garbage collected worlds. The good news is that since this is impacting the underlying core infrastructure, many built-in COM components including IE8 DOM and custom COM components can take advantage of this.

If you are a web developer, you would have certainly used Firebug or Visual Studio for debugging web applications. Web developers can get started with Visual Web Developer Express for basic debugging or can leverage the power of Visual Studio Team System which is meant for complex testing and debugging scenarios. While we cover the whole spectrum through the Visual Studio family, one of the experiences lacking in Internet Explorer is a built-in JScript debugger. The IE8 Developer Tools now offer an integrated JScript debugger that provides the basic set of debugging features. We believe this compliments Visual Studio debugging experience and is an important step towards making JavaScript developers more productive.

We look forward to hearing about your experiences with JScript and IE8 Beta 1 for Developers.

Shreesh Dubey, Product Unit Manager, JScript

JScript Blog : MIX08

JScript in Internet Explorer 8 Beta 1 for Developers