Analysis of the principle of gesture sliding screen switching in HTML5 single page

<p id="viewport" class="viewport">

    <p class="pageview" style="background: #3b76c0" >

        <h3 >页面-1</h3>

    </p>

    <p class="pageview" style="background: #58c03b;">

        <h3>页面-2</h3>

    </p>

    <p class="pageview" style="background: #c03b25;">

        <h3>页面-3</h3>

    </p>

    <p class="pageview" style="background: #e0a718;">

        <h3>页面-4</h3>

    </p>

    <p class="pageview" style="background: #c03eac;">

        <h3>页面-5</h3>

    </p>

</p>

.viewport{

   width: 500%;

   height: 100%;

   display: -webkit-box;

   overflow: hidden;

   //pointer-events: none; //这句话会导致整个页面上的点击事件失效，如需绑定点击事件，请注掉

   -webkit-transform: translate3d(0,0,0);

   backface-visibility: hidden;

   position: relative;

}

/*手指放在屏幕上*/

document.addEventListener("touchstart",function(e){

   e.preventDefault();

   var touch = e.touches[0];

   startX = touch.pageX;

   startY = touch.pageY;

   initialPos = currentPosition;   //本次滑动前的初始位置

   viewport.style.webkitTransition = ""; //取消动画效果

   startT = new Date().getTime(); //记录手指按下的开始时间

   isMove = false; //是否产生滑动

}.bind(this),false);

/*手指在屏幕上滑动，页面跟随手指移动*/

document.addEventListener("touchmove",function(e){

   e.preventDefault();

   var touch = e.touches[0];

   var deltaX = touch.pageX - startX;

   var deltaY = touch.pageY - startY;

   //如果X方向上的位移大于Y方向，则认为是左右滑动

   if (Math.abs(deltaX) > Math.abs(deltaY)){

       moveLength = deltaX;

       var translate = initialPos + deltaX; //当前需要移动到的位置

       //如果translate>0 或 < maxWidth,则表示页面超出边界

       if (translate <=0 && translate >= maxWidth){

           //移动页面

           this.transform.call(viewport,translate);

           isMove = true;

       }

       direction = deltaX>0?"right":"left"; //判断手指滑动的方向

   }

}.bind(this),false);

/*手指离开屏幕时，计算最终需要停留在哪一页*/

document.addEventListener("touchend",function(e){

   e.preventDefault();

   var translate = 0;

   //计算手指在屏幕上停留的时间

   var deltaT = new Date().getTime() - startT;

   if (isMove){ //发生了左右滑动

        //使用动画过渡让页面滑动到最终的位置

        viewport.style.webkitTransition = "0.3s ease -webkit-transform";

        if(deltaT < 300){ //如果停留时间小于300ms,则认为是快速滑动，无论滑动距离是多少，都停留到下一页

            translate = direction == 'left'?

            currentPosition-(pageWidth+moveLength):currentPosition+pageWidth-moveLength;

            //如果最终位置超过边界位置，则停留在边界位置

            translate = translate > 0 ? 0 : translate; //左边界

            translate = translate < maxWidth ? maxWidth : translate; //右边界

        }else {

            //如果滑动距离小于屏幕的50%，则退回到上一页

            if (Math.abs(moveLength)/pageWidth < 0.5){

                translate = currentPosition-moveLength;

            }else{

                //如果滑动距离大于屏幕的50%，则滑动到下一页

                translate = direction == 'left'?

                currentPosition-(pageWidth+moveLength):currentPosition+pageWidth-moveLength;

                translate = translate > 0 ? 0 : translate;

                translate = translate < maxWidth ? maxWidth : translate;

            }

        }

        //执行滑动，让页面完整的显示到屏幕上

        this.transform.call(viewport,translate);

    }

}.bind(this),false);

//计算当前的页码

pageNow = Math.round(Math.abs(translate) / pageWidth) + 1;

setTimeout(function(){

    //设置页码，DOM操作需要放到子线程中，否则会出现卡顿

    this.setPageNow();

}.bind(this),100);