[JavaScript] Dispatching keyboard event

gistfile1.js

// gecko and  webkit
// details here https://developer.mozilla.org/en-US/docs/DOM/event.initKeyEvent

var keyboardEvent = document.createEvent("KeyboardEvent");
var initMethod = typeof keyboardEvent.initKeyboardEvent !== 'undefined' ? "initKeyboardEvent" : "initKeyEvent";


keyboardEvent[initMethod](
                   "keydown", // event type : keydown, keyup, keypress
                    true,     // bubbles
                    true,     // cancelable  
                    window,   // viewArg: should be window  
                    false,    // ctrlKeyArg  
                    false,    // altKeyArg
                    false,    // shiftKeyArg
                    false,    // metaKeyArg
                    40,       // keyCodeArg : unsigned long the virtual key code, else 0  
                    0         // charCodeArgs : unsigned long the Unicode character associated with the depressed key, else 0
);
document.dispatchEvent(keyboardEvent); 

/* a better way */

function fireKey(el,key)
{
    if(document.createEventObject)
    {
        var eventObj = document.createEventObject();
        eventObj.keyCode = key;
        el.fireEvent("onkeydown", eventObj);
        eventObj.keyCode = key;   
    }else if(document.createEvent)
    {
        var eventObj = document.createEvent("Events");
        eventObj.initEvent("keydown", true, true);
        eventObj.which = key; 
        eventObj.keyCode = key;
        el.dispatchEvent(eventObj);
    }
} 

//useful keyCodes
// left: 37
// up : 38
// right : 39
// down : 40
// ENTER : 13

link form line 2 is broken https://developer.mozilla.org/en-US/docs/DOM/event.initKeyEvent