Question

I’m trying to code the following JS in coffeescript:

x = 0;
if(node.offsetParent) {
  do {
    x += node.offsetLeft;
  } while(node = node.offsetParent);
}       

Here’s what i have so far, but the node seems to come back null

if node.offsetParent
  loop
    x += node.offsetLeft
    break if typeof (node = node.offsetParent) == "undefined"
x

Answer 1

The problem is simply that when a DOM element node has no offset parent, node.offsetParent is null, not undefined. And typeof null is 'object', not 'undefined'.

Why not take the same approach as the original JS loop, which simply checked node.offsetParent for falsy-ness? Then your code might look something like:

x = 0
if node.offsetParent
  loop
    x += node.offsetLeft
    break unless (node = node.offsetParent)
x

I’d also like to point out that while CoffeeScript has no do..while syntax, you can simply use a while loop in this case, making your if superfluous:

x = 0
while node.offsetParent
  x += node.offsetLeft
  node = node.offsetParent
x