Caveats with sync promises

examples.js

// Function returns promise for once window.document.readyState
// becomes interactivate.
function whenInteractive(window) {
  let { promise, resolve } = defer()
  let state = window.document.readyState;
  if (state === "complete") resolve(window)
  if (state === "interactive") resolve(window)
  else {
    window.addEventListener("DOMContentLoaded", function(event) {
      // Is current window?
      if (event.target === window.document) resolve(window)
    })
  }
}

// When window becomes interactive we're supposed to do some stuff
// but if `resolve(window)` does call doStuff in next tick window
// may get closed by then without us having chance to do anything.
whenInteractive(window).then(doStuff)


// Simple utility to handle button press
function whenEnterPressed(button) {
  let { promise, resolve } = defer()
  button.addEventListener("click", function(e) {
    resolve(e)
  })
  return promise
}


whenEnterPressed(goFullScreenButton).then(function() {
  // When full screen button is pressed we try to go fullscreen.
  myVideo.mozRequestFullScreen()
  // Unfortunately if callback is called in next tick we'll end
  // with an exception:
  // Request for full-screen was denied because Element.mozRequestFullScreen()
  // was not called from inside a short running user-generated event handler.
})