Trigger keyboard event in Javascript, works in OSX Chrome 58

keydown.js

// Based on http://stackoverflow.com/a/10520017/1307721
// which wouldn't work for my use-case on my Mac because metaKey would always be true, for some reason
// Adapted to override metaKey to false
Podium = {};
Podium.keydown = function(k) {
    var oEvent = document.createEvent('KeyboardEvent');

    // Chromium Hack
    Object.defineProperty(oEvent, 'keyCode', {
                get : function() {
                    return this.keyCodeVal;
                }
    });     
    Object.defineProperty(oEvent, 'which', {
                get : function() {
                    return this.keyCodeVal;
                }
    });

    var metaKey = false;

    Object.defineProperty(oEvent, 'metaKey', {
                get : function() {
                    return metaKey;
                }
    });

    if (oEvent.initKeyboardEvent) {
        oEvent.initKeyboardEvent("keydown", true, true, document.defaultView, false, false, false, false, k, k);
    } else {
        oEvent.initKeyEvent("keydown", true, true, document.defaultView, false, false, false, false, k, 0);
    }

    oEvent.keyCodeVal = k;

    if (oEvent.keyCode !== k) {
        alert("keyCode mismatch " + oEvent.keyCode + "(" + oEvent.which + ")");
    }

    document.body.dispatchEvent(oEvent);
}
// Podium.keydown(40) => arrowdown ; Podium.keydown(38) => arrowup

z-chrome-only-shortened-keydown.js

var keyCode = 40;
var e = document.createEvent('KeyboardEvent');
Object.defineProperty(e, 'keyCode', { get: function() { return keyCode; } });     
Object.defineProperty(e, 'which', { get : function() { return keyCode; } });
Object.defineProperty(e, 'metaKey', { get : function() { return false; } });
e.initKeyboardEvent("keydown", true, true, document.defaultView, false, false, false, false, keyCode, keyCode);
e.keyCodeVal = keyCode;
if (e.keyCode !== keyCode) { alert("keyCode mismatch " + e.keyCode + "(" + e.which + ")"); }
document.body.dispatchEvent(e);