如何提高卷轴魔法的速度

//First the variables our app is going to use need to be declared

//References to DOM elements
var $window = $(window);
var $document = $(document);
//Only links that starts with #
var $navButtons = $("nav a").filter("[href^=#]");
var $navGoPrev = $(".go-prev");
var $navGoNext = $(".go-next");
var $slidesContainer = $(".slides-container");
var $slides = $(".slide");
var $currentSlide = $slides.first();

//Animating flag - is our app animating
var isAnimating = false;

//The height of the window
var pageHeight = $window.innerHeight();

//Key codes for up and down arrows on keyboard. We'll be using this to navigate change slides using the keyboard
var keyCodes = {
    UP  : 38,
    DOWN: 40
}

//Going to the first slide
goToSlide($currentSlide);


/*
*   Adding event listeners
* */

$window.on("resize", onResize).resize();
$window.on("mousewheel DOMMouseScroll", onMouseWheel);
$document.on("keydown", onKeyDown);
$navButtons.on("click", onNavButtonClick);
$navGoPrev.on("click", goToPrevSlide);
$navGoNext.on("click", goToNextSlide);

/*
*   Internal functions
* */


/*
*   When a button is clicked - first get the button href, and then slide to the container, if there's such a container
* */
function onNavButtonClick(event)
{
    //The clicked button
    var $button = $(this);

    //The slide the button points to
    var $slide = $($button.attr("href"));

    //If the slide exists, we go to it
    if($slide.length)
    {
        goToSlide($slide);
        event.preventDefault();
    }
}

/*
*   Getting the pressed key. Only if it's up or down arrow, we go to prev or next slide and prevent default behaviour
*   This way, if there's text input, the user is still able to fill it
* */
function onKeyDown(event)
{

    var PRESSED_KEY = event.keyCode;

    if(PRESSED_KEY == keyCodes.UP)
    {
        goToPrevSlide();
        event.preventDefault();
    }
    else if(PRESSED_KEY == keyCodes.DOWN)
    {
        goToNextSlide();
        event.preventDefault();
    }

}

/*
*   When user scrolls with the mouse, we have to change slides
* */
function onMouseWheel(event)
{
    //Normalize event wheel delta
    var delta = event.originalEvent.wheelDelta / 30 || -event.originalEvent.detail;

    //If the user scrolled up, it goes to previous slide, otherwise - to next slide
    if(delta < -1)
    {
        goToNextSlide();
    }
    else if(delta > 1)
    {
        goToPrevSlide();
    }

    event.preventDefault();
}

/*
*   If there's a previous slide, slide to it
* */
function goToPrevSlide()
{
    if($currentSlide.prev().length)
    {
        goToSlide($currentSlide.prev());
    }
}

/*
*   If there's a next slide, slide to it
* */
function goToNextSlide()
{
    if($currentSlide.next().length)
    {
        goToSlide($currentSlide.next());
    }
}

/*
*   Actual transition between slides
* */
function goToSlide($slide)
{
    //If the slides are not changing and there's such a slide
    if(!isAnimating && $slide.length)
    {
        //setting animating flag to true
        isAnimating = true;
        $currentSlide = $slide;

        //Sliding to current slide
        TweenLite.to($slidesContainer, 1, {scrollTo: {y: pageHeight * $currentSlide.index() }, onComplete: onSlideChangeEnd, onCompleteScope: this});

        //Animating menu items
        TweenLite.to($navButtons.filter(".active"), 0.5, {className: "-=active"});

        TweenLite.to($navButtons.filter("[href=#" + $currentSlide.attr("id") + "]"), 0.5, {className: "+=active"});

    }
}

/*
*   Once the sliding is finished, we need to restore "isAnimating" flag.
*   You can also do other things in this function, such as changing page title
* */
function onSlideChangeEnd()
{
    isAnimating = false;
}

/*
*   When user resize it's browser we need to know the new height, so we can properly align the current slide
* */
function onResize(event)
{

    //This will give us the new height of the window
    var newPageHeight = $window.innerHeight();

    /*
    *   If the new height is different from the old height ( the browser is resized vertically ), the slides are resized
    * */
    if(pageHeight !== newPageHeight)
    {
        pageHeight = newPageHeight;

        //This can be done via CSS only, but fails into some old browsers, so I prefer to set height via JS
        TweenLite.set([$slidesContainer, $slides], {height: pageHeight + "px"});

        //The current slide should be always on the top
        TweenLite.set($slidesContainer, {scrollTo: {y: pageHeight * $currentSlide.index() }});
    }

}

body, div, p {
    margin: 0;
    padding: 0;
}

body {
    font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif;
    font-weight: 300;
    letter-spacing: 0.0625em;
}

a {
    text-decoration: none;
}

nav {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 100;
}

nav ul {
    list-style: none;
    text-align: center;
    margin-top: 30px;
}

nav ul li {
    display: inline-block;
    margin-right: 20px;
}

nav ul li:last-child {
    margin-right: 0;
}

#back-to-tutorial {
    margin-left: 100px;
}

nav a {
    position: relative;
    top: 0;
    padding: 10px 20px;
    font-weight: normal;
    font-size: 20px;
    text-align: center;
    border-radius: 4px;
    background-color: #FFFFFF;
    color: #83C78E;
    -webkit-box-shadow: none;
    -moz-box-shadow: none;
    box-shadow: none;
}

nav a.active {
    top: -4px;
    background-color: #69C773;
    color: #FFFFFF;
    -webkit-box-shadow: 0 4px 0 0 #51a65f;
    -moz-box-shadow: 0 4px 0 0 #51a65f;
    box-shadow: 0 4px 0 0 #51a65f;
}

.slides-container {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    z-index: 10;
}

.slide {
    position: relative;
    width: 100%;
    height: 100%;
    overflow: hidden;
}

.slide .centered {
    width: 60%;
    margin: 200px auto 0;
}

.slide .centered h1 {
    text-align: center;
}

.slide .centered p {
    text-align: center;
    margin-top: 20px;
    font-size: 20px;
}

#slide-1 {
    background-color: #FFFFFF;
}

#slide-2 {
    background-color: #45959b;
}

#slide-3 {
    background-color: #778899;
}

#slide-4 {
    color: #FFFFFF;
    background-color: #291F37;
}

.go-prev, .go-next {
    cursor: pointer;
    font-weight: bold;
    text-decoration: underline;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<!-- Popper JS -->
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/modernizr/2.8.3/modernizr.min.js" type="text/javascript"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.11.6/TweenLite.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.11.6/plugins/CSSPlugin.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/gsap/1.11.6/plugins/ScrollToPlugin.min.js"></script>
    
<nav>
    <ul>
        <li><a href="#slide-1">Slide 1</a></li>
        <li><a href="#slide-2">Slide 2</a></li>
        <li><a href="#slide-3">Slide 3</a></li>
        <li><a href="#slide-4">Slide 4</a></li>
    </ul>
</nav>

<div class="slides-container">
    <div class="slide" id="slide-1">
        <div class="centered">
            <h1>Fullscreen slides with GSAP</h1>
            <p>Let's go to the <span class="go-next">next slide</span>.</p>
        </div>
    </div>
    <div class="slide" id="slide-2">
        <div class="centered">
            <h1>It is so easy to navigate through slides</h1>
            <p>You can go back to <span class="go-prev">previous slide</span> or go to the <span class="go-next">next slide</span>.</p>
        </div>
    </div>
    <div class="slide" id="slide-3">
        <div class="centered">
            <h1>Use mouse wheel</h1>

            <p>No, really. Try to scroll up and down with the mouse wheel to switch between slides.</p>
        </div>
    </div>
    <div class="slide" id="slide-4">
        <div class="centered">
            <h1>... Or use keyboard arrows</h1>
            <p>You go to previous and next slide, using up and down keyboard arrows.</p>
        </div>
    </div>
</div>