Javascript - trigger specific keyboard keys

Question

I have this piece of code:

window.addEventListener('keydown', function (e) { 
   console.log(e.which); 
   console.log(e.keyCode); 
});

 var evObj = new KeyboardEvent('keydown', {key:65});
 window.dispatchEvent(evObj);

Why i see 0 in console and not 65 ??

Also both e.keyCode and e.which are 0 and not 65, i am on Chrome latest version

thank you a lot.

Answer 1

There is a bug in chrome, keyCode and which are not configurable.

Possible workarkaround: define a custom getter

 window.addEventListener('keydown', function (e) { console.log(e.which); });
 
 (function(o,k){
    //use createEvent for better compatibility
   var evObj = document.createEvent('HTMLEvents');
    evObj.initEvent('keydown', true, false);
    Object.defineProperty(evObj, 'keyCode', {
      get: function() {
        return k;
      }
    });
    Object.defineProperty(evObj, 'which', {
      get: function() {
        return k;
      }
    });
    o.dispatchEvent(evObj); 
 }(window,65));

Answer 2

Also both e.keyCode and e.which are 0 and not 65, i am on Chrome latest version

Because you're setting key, not keyCode and which. According to MDN, key is a representation of the key, not a keycode. To initialize keyCode and/or which, you should...do that (see MDN's article on KeyboardEvent).

var evObj = new KeyboardEvent('keydown', {keyCode:65, which:65});

Here's an example, but it doesn't appear to work in Chrome (still get 0) — that's a Chrome bug, workaround below. Does work in Firefox. Fails in IE11 because IE11 doesn't like new KeyboardEvent:

window.addEventListener("keydown", function(e) {
  snippet.log("keyCode = " + e.keyCode + ", which = " + e.which);
}, false);
setTimeout(function() {
  var evObj = new KeyboardEvent('keydown', {keyCode:65, which:65});
  snippet.log("Sending event");
  window.dispatchEvent(evObj);
}, 300);

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

You can work around the Chrome bug using the technique from this answer:

window.addEventListener("keydown", function(e) {
  snippet.log("keyCode = " + e.keyCode + ", which = " + e.which);
}, false);
setTimeout(function() {
  var evObj = new KeyboardEvent('keydown', {keyCode:65, which:65});
  // Chrome bug workaround:
  if (evObj.keyCode != 65) {
    Object.defineProperty(evObj, "keyCode", {
      value: 65
    });
    Object.defineProperty(evObj, "which", {
      value: 65
    });
  }
  snippet.log("Sending event");
  window.dispatchEvent(evObj);
}, 300);

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>