Key timer function for reliable input, for use in games and similiar. Originally not mine, but this version uses `addEventListener`.

KeyboardController

function KeyboardController(keys, repeat) {
    var timers = {};

    document.addEventListener('keydown', function(event) {
        var key = event.keyCode;
        if (!(key in keys))
            return true;
        if (!(key in timers)) {
            timers[key] = null;
            keys[key](event);
            if (repeat!==0) {
                timers[key] = setInterval(keys[key], repeat);
            }
        }
        return false;
    }, false);

    document.addEventListener('keyup', function(event) {
        var key = event.keyCode;
        if (key in timers) {
            if (timers[key]!==null)
                clearInterval(timers[key]);
            delete timers[key];
        }
    }, false);

    window.addEventListener('blur', function() {
        for (key in timers)
            if (timers[key]!==null)
                clearInterval(timers[key]);
        timers= {};
    }, false);
}; //from stackoverflow: http://stackoverflow.com/a/3691661/1749791