Just a Theory

By David E. Wheeler

Posts about JScript

Quirks of IE's JavaScript Implementation

Just a few notes about the quirks of IE’s JavaScript implementation that I had to figure out and work around to get TestSimple working in IE.:

  • IE doesn’t like serial commas. In other words, If I create an object like this:

    var obj = {
        foo: "yow",
        bar: "bat",

    IE will complain. It seems it doesn’t like that last comma, but it doesn’t give you a decent diagnostic message to help you figure out that that’s what it doesn’t like. Fortunately, I didn’t have to figure this one out; Marshall did And now I know to expect that IE thinks that its JavaScript should parse like SQL. Whatever!

  • You can’t truncate an array using a single argument to splice(). In Firefox, ary.splice(0) will truncate the array, but in IE, you must provide the second argument, like this: ary.splice(0, ary.length)—or else it won’t actually truncate the array.

  • Many IE JavaScript functions don’t seem to actually inherit from the Function class! I discovered this when I tried to call document.write.apply() and it failed. Not only does the apply() method not exist, but I can’t even add it! I came up with a decent workaround for this problem in TestBuilder, but I still don’t have a general solution to the problem. I did find a page that might have a general solution, but it sure is ugly.

  • IE automatically converts line endings in to the platform specific alternatives whenever you assign a JavaScript string to a text element. When Marshall showed me output that wasn’t properly adding “#” after all line endings, this was my immediate suspicion, and a quick Googling confirmed the issue. So I had to add regular expressions to look for all variations on the line endings.

I’m sure I’ll notice other issues as I work more with JavaScript, but feel free to chime in here with any gotchas you’ve noticed, and then I won’t have to work so hard to figure them out on my own in the future (and neither will you)!

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