Relativize that thing: todays CSS war story

Today, I had a seemingly simple problem: position a floating label element inside of a text input field, inside a elastic layout. To achieve an effect like:

Moreover, I wanted to implement this as a generic javascript widget that I can reuse throughout the application. This was hard, real hard.

At first, I just used position: absolute and set the position of the label relative the the root document, getting the coordinates required from the position and dimension of the companion text field. Well, this didn't work so well when the window is resized. Too bad we got an elastic layout, if we had a fixed width one I would have been done. My quick and dirty solution was to register the window.onresize callback and reset the positions of the labels whenever the window is resized. This actually worked well in IE, but not so in FF. The problem with FF is that the callback is invoked too sparsely, it's just not responsive enough when you are just dragging the corner of the window around, but you see these labels in all the wrong places while you are dragging around the corner of the browser until you leave your mouse still for a second, at which point the labels receive the event and jump to where they should be. This just plain looks bad, and although your users probably won't resize the window too much, I think it will definitely give the impression of a cheesy app.

So, my first attempt at a work around is a brute force one. I wrote my onresize callback functionality for FF that is more responsive. Here was the code.

 /* this is a funny hack in FF to get window resize events more often */
var ffonresize = function(){
    var listeners = [];
    var dim = document.viewport.getDimensions();
    var pe = null;
    pe = new PeriodicalExecuter(function(pe) {
        var nd = document.viewport.getDimensions();
        if (!(nd.width == dim.width && nd.height == dim.height)){
            dim = nd;
    }, 0.2);
    return function(listener){
if (Prototype.Browser.Gecko)
    Event.observe(window, 'resize', this.__onResize);

This improved the situation, but... not good enough. Then I thought, there must be a way with position: relative to do it. After all, isn't that what it's for?

I tried making the label element position: relative, but this didn't work: you could shift the position of the element relative to where it would have been, but the space for where it would have been is still taken up, and now it's an empty space...
I did some research. One of the best resources is quirksmode again, this is also a helpful article. It turns out the common practice to use is to have a container that is relative and then a child under it that is absolute, which will cause the child to use the parent's position as the reference point. But trying the things out didn't work at first. After some trial and error, I figured out that, not only does the parent have to be position: relative, it also had to be display: block. My parent container happened to be table cells, so I either had to set their display to block or add a div under them. Setting their display to block didn't work for me because it completely messed up the layout of the table, so I had to go with the second method.

Adding the div was annoying because not only did I have to go to a few different places in the app to add the markup, it also made my widget depend on more. Of course, I guess I could inject the div dynamically, but I haven't tried that yet. So, this worked, I no longer had to use the onresize callback and reset the position of the labels, I just set:

position: absolute;
top: 2px;
right: 5%;

Top of 2px to give the top some space, right of 5% to give enough space for the label. Both are relative to the divs I newly added. Well, this kinda worked... except for my short textfields. See, I had long text fields that take up almost 100% of the width of the parent, but also shorter ones that take up about 60%, so while it worked well for the long textfield, sitting right inside it on the right edge, it was well outside of the short textfields. I wanted to use javascript to figure out what's the % of the width of the text field, which I could use to calculate where the label should be, but that number is in my css, and using javascript you can only get dimensions in terms of pixels, i.e., all the percentage info is lost.

What to do? Well, I calculated the percentage by doing a division between the text field and its parent's width in pixels, this is my code(using prototype.js):

right: (1 + 100 * (1 - this.field.getWidth() / 
    this.field.up().getWidth())) + "%"

Yeah, it's pretty crazy, but it worked, beautifully. It works in IE7, FF3, and Safari, didn't work in Opera, but that could have been because other javascript bugs I had wrt Opera.

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