Fastest way to find the index of a child node in parent

Answer 1

Generally speaking, a small difference in performance has a negligible effect unless the code is run in a loop. Having to run the code once instead of every time will be significantly faster.

Do something like this once:

var par = document.getElementById('parent');
var childs = par.getElementsByTagName('*');
for (var i=0, len = childs.length;i < len;i++){
  childs[i].index = i;
}

Subsequently finding the index is as easy as:

document.getElementById('findme').index

It sounds like whatever you're doing could be benefited by having a cleaner relationship between the DOM and the javascript. Consider learning Backbone.js, a small javascript MVC library which makes web applications much easier to control.

edit: I've removed the jQuery I used. I do normally avoid using it, but there's quite a preference for it on SO, so I assumed it would end up being used anyway. Here you can see the obvious difference: http://jsperf.com/sibling-index/8