jethrolarson

O(1) - Trivial, we've done something almost exactly like this and it wont take long to complete at all
O(log n) - Need to add a small capability then it's copy-pasta
O(n) - Simple, It's like things we've done before. No refactoring or architectural changes needed.
O(n^2) - Going to need to rework some things and watch out for regressions
O(n!) - Major rework needed, lots of risk
O(MG) - This is so complex or ill-defined that it may never complete

OrganicPanda

// Demo: http://jsfiddle.net/pFaSx/

// Create an invisible iframe
var iframe = document.createElement('iframe');
iframe.id = "hacky-scrollbar-resize-listener";
iframe.style.cssText = 'height: 0; background-color: transparent; margin: 0; padding: 0; overflow: hidden; border-width: 0; position: absolute; width: 100%;';

// Register our event when the iframe loads
iframe.onload = function() {
  // The trick here is that because this iframe has 100% width