Archive for May, 2009

Determining browsers’ rendering and JavaScript engine versions


Now that I’ve updated and found a permanent home for the Browser Compatibility Cheat-Sheet, I thought I’d take the time to share the method to my madness for excavating the rendering engine and JavaScript data from browsers (these are the details in the cheat-sheet). If you’re asking yourself “Why do I care Brent?” then I urge you to watch my screencast on Browser Compatibility Testing Risk Analysis. My answer to your question in a nutshell is that you need to care as a developer or tester because fully understanding how browsers work, knowing how similar and different they are, and being able to quickly assess how a feature or change to a Web application will impact your development, testing or regression. I’ll leave it at that for now.

It’s never really been quick or easy when I mine the data (which seems to be about once a year), but when I reassess the cheat-sheet I typically spend most of the time re-reminding myself of how to gather the info for the various browsers, all the while discovering new sources. Here is my high-level browser info excavating process:

  1. Get the info from the browser itself:
    1. Install it
    2. Look at the browser download site, FAQ, & Release Notes
    3. Look at the user-agent string at
    4. Look at the installed assembly version numbers and text files
    5. Look at the Help/About section
    6. Look at comments in source control and source code (if available)
  2. Search the web
    1. Look at keywords on wikipedia (Netscape, V8, WebKit, etc) . Wikipedia has gained a lot of browser data in the last couple years, some of my favorite and most useful links are comparison of layout engines & Browser Timeline
    2. Search by keywords, and look at articles and comments on the Web

And on to a few lower-level details for a few of the most popular browsers:

Internet Explorer

  1. Rendering Engine: Trident being the name of the IE rendering engine, it was once believed that the version of Trident matched the the version of the MSHTML.dll found at C:\windows\System32\. But with IE 8.0, the IE team has a reference on their blog that rendering engine in 8.0 is Trident 4.0 which can now be found in the user-agent string. This version conflicts with prior data I had gathered but we’ll run with it.  Hopefully, from here on out you can just gather the version from the user-agent string, only time will tell. Here is an example user-agent string for IE8: “Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0;)
  2. JavaScript Engine: JScript is the JavaScript engine in IE, the file version of JScript.dll found in C:\windows\System32\ will give you version number.


  1. Rendering Engine: Webkit is the rendering engine for Chrome. To get the rendering engine version, in the browser URL bar just type “About:”. The version will follow the “Webkit:” key. Notice that the User Agent contains the same Webkit number, hence the rendering engine version can be gathered from the User Agent string also.
  2. JavaScript Engine: V8 is the JavaScript engine for Chrome. The version is listed in the same place as the rendering engine and is the number following the “V8:” key.


  1. Rendering Engine: Firefox uses the Gecko rendering engine and the version number can be found in the user-agent string (can be seen by typing “about:” in the URL bar or going to Help->About in the menu). For example in the following string: “Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv: Gecko/2009042316 Firefox/3.0.10”, the “rv:” is the version and the “2009042316” build number. 
  2. JavaScript Engine: Firefox’s JavaScript engine is SpiderMonkey and I’ve never found references to version numbers. From what I understand the JavaScript engine is compiled to JS3250.dll in \program files\mozilla firefox (js3250.lib on Linux), but the version number never changes on it even though the date and size do, which makes tracking here fairly useless. I’ve always gathered ECMA compatibility data from official release notes as well as using the value for “JavaScriptVer ” key found when visiting (click the ‘more’ link in top-right corner to get this detail).


  1. Rendering Engine: Webkit is the rendering engine in Safari and the version can be found in the user-agent string. For example in the string: “Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Safari/528.17” the version number is 528.18. This can also be seen on the webkit.dll file property “Product Version” in Windows (\program files\safari\).
  2. JavaScript Engine: With Safari 4.0 and up the JavaScript engine is new and named Nitro. At this time of writing 4.0 is still in beta and I see no official version for Nitro, but hopefully we’ll find a reference once it comes out of beta. Regarding past versions for their old engine JavaScriptCore, I’ve never found version numbers so I only documented the JavaScript ECMA compatibility found at various places on the web as well as the value for “JavaScriptVer ” key found when visiting (click the ‘more’ link in top-right corner to get this detail).


And there you have it, the method to my madness. If you have differing or better data please feel free to add it in a comment.

Browser Compatibility Cheat-Sheet


Browser Compatibility Cheat Sheet This link/post will serve as the official place for the Browser Compatibility Cheat-Sheet and the post can be permanently accessed from the side navigation. Any new updates/links to the cheat-sheet will be put in this post.

What is the Browser Compatibility Cheat-Sheet?

The cheat-sheet is a list of browsers’ rendering engine and JavaScript engine versions. This reference provides testers a quick and easy way to view groupings of browsers and their versions to help determine testing redundancy and trim the “browsers to test” list. For further explanation and details watch the screencast: Browser Compatibility Testing Risk Analysis.

Download the latest Browser Compatibility Cheat-Sheet here (zipped Excel file): (8.74 KB)

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