polling.js

var poll = function (sel, fn, t) {
  t = t || 25; // 25ms default
  var $el = $(sel), found = $el.length;

  // Proper tail calls - return and pass all necessary variables
  // i.e. minimize current frame's footprint (allow release / reuse in es6 env)
  if (found) return fn.call($el);
  else if (document.readyState === 'complete') return;
  else return setTimeout(function() {
    poll(sel, fn, t);
  });
};