This is how I managed to facilitate keyboard events in multiple browsers

keyup_event.js

// <input id="my-input-element" type="text" value="foo"/>
var evt, node = document.getElementById('my-input-element');

// Have to use dispatchEvent/fireEvent because jQuery.trigger will not
// fire an event attached via addEventListener. Each environment has an
// unusual way to trigger a keyup event.
if (node.dispatchEvent) {
  // Sane browsers
  try {
    // Chrome, Safari, Firefox
    evt = new KeyboardEvent('keyup');
  } catch (e) {
    // PhantomJS (wat!)
    evt = document.createEvent('KeyboardEvent');
    evt.initEvent('keyup', true, false);
  }
  evt.keyCode = 32;
  node.dispatchEvent(evt);
} else {
  // IE 8
  evt = document.createEventObject('KeyboardEvent');
  evt.keyCode = 32;
  node.fireEvent('onkeyup', evt);
}

Isn't keyCode as read only property

https://stackoverflow.com/a/26979893. This works for me.

var keyPressed = null;

function keyPress(key) {
  var event = document.createEvent('Event');
  event.keyCode = key; // Deprecated, prefer .key instead.
  event.key = key;
  event.initEvent('keydown');
  document.dispatchEvent(event);
}

document.addEventListener('keydown', function(e){
   keyPressed = e.key;
});

keyPress(37)
alert(keyPressed);