Make function wait until element exists

Question

I\'m trying to add a canvas over another canvas – how can I make this function wait to start until the first canvas is created?

function PaintObject(brush) {         


        

Answer 1

Depending on which browser you need to support, there's the option of MutationObserver.

EDIT: All major browsers support MutationObserver now.

Something along the lines of this should do the trick:

// callback executed when canvas was found
function handleCanvas(canvas) { ... }

// set up the mutation observer
var observer = new MutationObserver(function (mutations, me) {
  // `mutations` is an array of mutations that occurred
  // `me` is the MutationObserver instance
  var canvas = document.getElementById('my-canvas');
  if (canvas) {
    handleCanvas(canvas);
    me.disconnect(); // stop observing
    return;
  }
});

// start observing
observer.observe(document, {
  childList: true,
  subtree: true
});

N.B. I haven't tested this code myself, but that's the general idea.

You can easily extend this to only search the part of the DOM that changed. For that, use the mutations argument, it's an array of MutationRecord objects.