Javascript polling functions

polling-callback.js

// The polling function
function poll(fn, callback, timeout, interval) {
  var endTime = Number(new Date()) + (timeout || 2000);
  interval = interval || 100;

  (function p() {
    // If the condition is met, we're done!
    if (fn()) {
      callback();
    }
    // If the condition isn't met but the timeout hasn't elapsed, go again
    else if (Number(new Date()) < endTime) {
      setTimeout(p, interval);
    }
    // Didn't match and too much time, reject!
    else {
      callback(new Error('timed out for ' + fn + ': ' + arguments));
    }
  })();
}

// Usage: ensure element is visible
poll(function () {
  return document.getElementById('lightbox').offsetWidth > 0;
}, function (err) {
  if (err) {
    // Error, failure callback
  }
  else {
    // Done, success callback
  }
}, 2000, 150);

polling-deferred.js

// The polling function
function poll(fn, timeout, interval) {
  var dfd = new Deferred();
  var endTime = Number(new Date()) + (timeout || 2000);
  interval = interval || 100;

  (function p() {
    // If the condition is met, we're done!
    if (fn()) {
      dfd.resolve();
    }
    // If the condition isn't met but the timeout hasn't elapsed, go again
    else if (Number(new Date()) < endTime) {
      setTimeout(p, interval);
    }
    // Didn't match and too much time, reject!
    else {
      dfd.reject(new Error('timed out for ' + fn + ': ' + arguments));
    }
  })();

  return dfd.promise;
}

// Usage: ensure element is visible
poll(function () {
  return document.getElementById('lightbox').offsetWidth > 0;
}, 2000, 150);