title: Checking if iframe is ready to be written to
body: <p>A 3rd party script on my web page creates an iframe. I need to know when this iframe is ready, so I can manipulate its DOM.</p>
  
  <p>I can think of a hacky approach: repeatedly try to modify the iFrame's DOM, and return success when a change we make sticks between two attempts. For this to work, I would prefer a property I can check on the iframe repeatedly.</p>
  
  <p>Is there an alternative, cross-browser <em>evented</em> approach to knowing that the iframe is ready? E.g. can we redefine the onLoad function to call into our code (but I don't know if I can do this, since I didn't create the iframe).</p>