Javascript polling functions

polling.js

// deferred
function poll(fn, timeout, interval) {
  let endTime = Number(new Date()) + (timeout || 2000)
  interval = interval || 100

  let checkCondition = (resolve, reject) => {
    // If the condition is met, we're done! 
    let result = fn()

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

  return new Promise(checkCondition)
}

poll(() => {
	return document.getElementById('lightbox').offsetWidth > 0
}, 2000, 150).then(() => {

}).catch(() => {

})


/* *** */

// without deferred
function poll(fn, callback, errback, timeout, interval) {
  let endTime = Number(new Date()) + (timeout || 2000)
  interval = interval || 100

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

poll(() => {
  return document.getElementById('lightbox').offsetWidth > 0
  }, () => {
    // Done, success callback
  }, () => {
    // Error, failure callback
  }
)