JS: idle timer with callback

idle.js

( function() {

    var timeoutDuration = 30;
    var mouseMoved      = 0;
    var keyPressed      = 0;

    var getDocument = function() {
        if ( window ) {
            return window.document;
        }
        return document;
    }

    var setDuration = function( duration ) {
        this.timeoutDuration = duration;
    };

    var init = function() {
        console.log("init");
        getDocument().addEventListener( 'DOMContentLoaded', onDocumentLoaded );
    };

    var onDocumentLoaded = function() {
        console.log("onDocumentLoaded");
        getDocument().onmousemove = onMouseMoved;
        getDocument().onkeydown   = onKeyPressed;
    };

    var onMouseMoved = function( event ) {
        console.log( "onMouseMoved" );
        this.mouseMoved = new Date();
    };

    var onKeyPressed = function( event ) {
        console.log( "onKeyPressed" );
        this.keyPressed = new Date();
    };

    init();

} )();