Question

Oftentimes in the web development community, you hear people complaining about developing for IE6. However, if you are developing using a robust JavaScript framework like jQuery, is developing for IE6 any different than developing for IE7?

Answer 1

I’ll add a few points which haven’t been listed:

1. CSS width strictly adhered to: IE7 in standards compliance now mode strictly interprets width styles in CSS. In IE6, if you have a child element that has a width which is greater than the parent element, it would often ignore the width declaration of the parent and expand to fit the child, often requiring hacks of overflow: hidden to make sure the parent didn’t expand.

   This is mostly a good thing, but unfortunately introduces a number of other quirks, e.g. <table style="width: 100%"> in a scrolled DIV with CSS overflow set to overflow: auto or scroll will expand the table to the width of the scrolled DIV including the width of the vertical scrollbar so some of the table will be cut off by the scroll bar on the right.

2. Cleartype with DirectX filters disabled: IE7 disables cleartype (font smoothing on LCD monitors) for elements which have DirectX filters such as alpha transparency and gradients. This is good in some ways, as cleartype made elements with filters, especially bolded ones very blurry/fuzzy, but it’s bad because it now renders the text blocky and aliased on LCDs.

   IE7 I think also now supports alpha: 1.0 as well as filter: alpha(opacity=100)

3. SELECT z-index bug fixed: IE7 fixed a bug where the SELECT elements have infinite z-index and are always above other elements unless you put an IFRAME in between of the SELECT and the element you want to display above it. This is a problem for menus etc.

4. CSS pseudo-classes improvements: :hover and some other similar CSS states are now supported outside of hyperlinks.

5. Performance not necessarily improved: IE7 introduced many bugs in it’s VML engine, and in IE8 VML is now 10x slower than in IE7 when in standards compliance mode, so it’s not altogether good. In addition, I have test cases which show that finding offsetLeft and offsetTop in mouse events in standards compliance mode in IE7 can also be around 10x slower in my web app.

   IE in quirks mode though it’s about the same performance for VML and offsetLeft/Top throughout IE6, 7+8. My experience in IE7 standards compliance mode is it’s actually much slower than standards compliance mode in IE6, though it is definitely much more compliant.

   I think it’s a bit of a double-edged sword though, as raw JavaScript performance did improve, so things like working with array methods and for loops did improve even though I think the rendering engine and many of the associated DOM methods became much slower in standards compliance mode in IE7+.