Question

Can someone tell me why this won’t work?

var top = 0;
for (divToPosition in $('.positionableDiv')) {
   divToPosition.css('top',top+'px');
   top = top + 30;
}

Answer 1

The first reason would be the misuse of the for loop.

jQuery has an idiom for looping over selected elements..

var top = 0;
$('.positionableDiv').each(function() {
   $(this).css('top',top+'px');
   top = top + 30;
});

Please take a look at for…in for a better understanding of the way a for…in loop works in javascript, it does not enumerate in the same way as say .NET or Java.

From Article:

Although it may be tempting to use this as a way to iterate over an Array, this is a bad idea.