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InelegantJavaScript
Inelegant JavaScript
A collection of bad things about JavaScript, such as buggy language implementation gotchas and quirks, especially in browsers. -- SteveYen
- Where's my memory? delves into Internet Explorer's JavaScript implementation (also known as JScript), which '''leaks memory when using closures'''.
- Actually, it's more about COM/DOM objects in a deadly circular embrace with JavaScript objects.
- Also http://jgwebber.blogspot.com/2005/01/dhtml-leaks-like-sieve.html
- Flash's version of JavaScript, aka ActionScript, is different.
- Shockingly '''ActionScript does not support closures''' (in Flash Players prior to version 6).
- Here's the description and workaround.
- '''ActionScript does not support eval()'''.
- Or, eval() in ActionScript can only do variable lookups, not true expressions.
- '''ActionScript does not support dynamic regular expressions using the RegExp object'''.
- http://livedocs.macromedia.com/flash/mx2004/main_7_2/wwhelp/wwhimpl/common/html/wwhelp.htm?context=Flash_MX_2004&file=00000756.html#comments
- These issues will make it very very hard to impossible to get TrimPath technology to work in Flash/ActionScript.
- Maybe things have changed, though, in Flash 8 or beyond (Apollo/AIR)
- Laszlo implementation of EcmaScript...
- Documented differences can be found here.
- Laszlo EcmaScript limitations might be same as ActionScript limitations (since Laszlo deploys to Flash runtime)?
- Internet Explorer and Mozilla treat JavaScript '''objects and arrays''' shortcut syntax differently.
- The below code with the extra trailing commas works in Mozilla JavaScript engines (Spider Monkey and Rhino). But it causes an exception in Internet Explorer. Too bad -- it actually made programming easier, not having to mentally treat the last item differently.
- var x = { slot1: 123, slot2: 456, };
- var y = [ 1, 2, 3, ];
- '''String.split()''' with regular expressions is different in IE and Mozilla/Firefox. Type the following into your browser's URL location bar...
- javascript:"a${b}c".split(/(\$\{[^\}]+\})/g)
- Mozilla/Firefox returns "a,${b},c" -- I prefer this return style.
- IE returns "a,c" -- this seems lossy to me, ignoring the capture parenthesis in the regular expression.
- If you type in "javascript:"a${b}c".split(/\$\{[^\}]+\}/g)", you get "a,c" in both browsers.
- You also can't trust the edge cases of the expression appearing at the start and end of the string or right next to each other.
- The upshot is not to use the parenthesis and test everything. Or, don't use regular expressions.
- Here's a comparison table...
| URL code | Mozilla/Firefox | IE |
| javascript:"a${b}c".split(/(\$\{[^\}]+\})/g) | a,${b},c | a,c |
| javascript:"a${b}".split(/\$\{[^\}]+\}/g) | a, | a |
| javascript:"${b}c".split(/\$\{[^\}]+\}/g) | ,c | c |
| javascript:"a${b}${c}d".split(/\$\{[^\}]+\}/g) | a,,d | a,d |
- '''eval() and function differences'''
| URL code | Mozilla/Firefox | IE |
| javascript:function(){return 111} | nothing! | nothing! |
| javascript:(function(){return 111}) | function () { return 111; } | nothing! |
| javascript:eval("function(){return 111;}") | nothing! | nothing! |
| javascript:eval("var s=function(){return 111};s") | function () { return 111; } | function(){return 111} |
- String charAt works in IE and Mozilla (str.charAt(index)).
- '''Do not rely on strindex''' array-based-syntax shortcut syntax, which might not work in IE.
- Be wary of using undefined global variables in IE.
- Another blog entry from Eric Lippert explains why.
DOM Related Quirks
- innerHTML doesn't work in IE for TABLE elements, but works for Mozilla/Firefox.
- Other resources
- PPK has a quirksmode section for JavaScript quirks across various browsers
- I recommend O'Reilly's '''JavaScript and DHTML Cookbook''' highly.
See also: ElegantJavaScript
<<Be wary of using undefined global variables in IE Another blog entry from Eric Lippert explains why.>>
Link is broken, but I think this is it:
http://blogs.msdn.com/ericlippert/archive/2006/05/04/590030.aspx