CSS Expressions

Question

I read somewhere that CSS Expressions were deprecated and shouldn't even be used. I had never heard of them and decided to take a look. I found a code example that kept a floating element in the same spot on the screen, even if you scrolled.

<html>
<style>
#fixed {
position:absolute;
left:10px;
top:expression(body.scrollTop + 50 + "px");
background:white;
border:1px solid red;}
</style>
<body>
<p id="fixed">Here is some text, which is fixed.</p>
<p>
[many times: "stuff <br/>"]
</p>
</body>
</html>

This reminded me of the sites that had the "share bars" and stuff at the bottom of their pages.

So...

Is this how they are doing it?
Is it alright to use Expressions in this situation?
If not, what should I use?
Are there any other interesting/helpful things that expressions can help with?

Google Chrome says otherwise ;) The code snippet worked fine in my Google Chrome browser. — Freesnöw, May 31 '11 at 18:16
JavaScript is far more flexible and ubiquitous than css expressions — user229044, May 31 '11 at 18:17
We can use them to emulate support for [`calc`](http://caniuse.com/#feat=calc) in old IE browsers with the css `expression` syntax. — user3459110, Sep 02 '14 at 18:07
http://www.w3schools.com/cssref/css_functions.asp -> might replace expressions — Randy, May 25 '16 at 14:24

score 65 · Accepted Answer · answered May 31 '11 at 18:13

CSS expressions used to work in older IE's, but they have been completely abandoned in IE8:

Dynamic properties (also called "CSS expressions") are no longer supported in Internet Explorer 8 and later, in IE8 Standards mode and higher. This decision was made for standards compliance, browser performance, and security reasons, as detailed in the IE blog entry titled Ending Expressions. Dynamic properties are still available in Internet Explorer 8 in either IE7 mode or IE5 mode.

So it's arguably not really worth learning them any more.

If not, what should I use?

Depending on the use case, JavaScript or media queries.

As @Yet Another Geek notes, your above example can be implemented using position: fixed. IE6 doesn't support that - the CSS expression was probably created to work around that.

Link to the Ending Expressions blog entry: https://blogs.msdn.microsoft.com/ie/2008/10/16/ending-expressions/ — dzz, Dec 20 '19 at 19:50

score 15 · Answer 2 · answered May 31 '11 at 18:15

For keeping an element in the same place while scrolling you should use the position:fixed property and then use top,bottom,left and right properties to tell where it should be positioned.

EDIT: Here how it should be for your example:

<html>
<style>
#fixed {
position:fixed;
left:10px;
top: 50px;
background:white;
border:1px solid red;}
</style>
<body>
<p id="fixed">Here is some text, which is fixed.</p>
<p>
[many times: "stuff <br/>"]
</p>
</body>
</html>

score 11 · Answer 3 · answered May 31 '11 at 18:17

Probably not. It's easier to use position:fixed or Javascript
Not unless you're only supporting IE < 8. IE8+ and other browsers don't support it*; it's not standards compliant and won't pass validation
Use position:fixed; bottom:x; top:y; left: a; right:b; where x, y, a, and b are offsets. Or, use Javascript
Again, not unless you're using old versions of IE only. Really, just dump it. the same effects can be achieved with JS and normal CSS.

*Officially, anyways. Apparently it worked on Chrome for @DalexL

CSS Expressions

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