document.addEventListener('DOMContentLoaded', function() {

    //动态创建回到首页dom

    var backDom = document.createElement("div");

    backDom.className = "z-back";

    backDom.innerHTML = '<a href="/"><svg class="icon-back" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg"><path fill="#ffffff" d="M879.461 517.238l-366.588-336.911-368.334 335.167c-6.983 6.983-6.983 17.457 0 24.441s17.457 6.983 24.441 0l343.894-314.219 343.894 314.219c3.492 3.492 6.983 5.238 12.219 5.238s8.726-1.745 12.219-5.238c5.238-5.238 5.238-15.712-1.745-22.695zM767.739 524.219c-10.474 0-17.457 6.983-17.457 17.457v267.084h-143.143v-186.784h-190.277v186.784h-143.143v-267.084c0-10.474-8.726-17.457-17.457-17.457-10.474 0-17.457 6.983-17.457 17.457v301.997h214.715v-186.784h118.704v186.784h214.715v-301.997c-1.745-10.474-8.726-17.457-19.202-17.457zM642.051 274.591h106.484v92.519c0 10.474 8.726 17.457 17.457 17.457 10.474 0 17.457-6.983 17.457-17.457v-127.433h-143.143c-10.474 0-17.457 6.983-17.457 17.457 1.745 8.726 10.474 17.457 19.202 17.457z"  /></svg></a>';

    document.body.appendChild(backDom);

    //回到首页拖拽效果

    //获取屏幕宽高

    var screenW = window.screen.availWidth;

    var screenH = window.screen.availHeight;

    var dragBox = document.querySelector(".z-back");

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

        var touch = e.touches[0];

        startX = touch.pageX;

        startY = touch.pageY;

        var left = getCss(dragBox, "left");

        var top = getCss(dragBox, "top");

        var width = getCss(dragBox, "width");

        var height = getCss(dragBox, "height");

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

            e.preventDefault();

            var touch = e.touches[0];

            var x = touch.pageX - startX;

            var y = touch.pageY - startY;

            var nowLeft = left + x;

            var nowTop = top + y;

            //边界值处理

            if(x > 0){

                nowLeft = nowLeft > screenW - width ? screenW - width : nowLeft;

            }else{

                nowLeft = nowLeft > 0 ? nowLeft : 0;

            }

            if(y > 0){

                nowTop = nowTop > screenH - height ? screenH - height : nowTop;

            }else{

                nowTop = nowTop > 0 ? nowTop : 0;

            }

            dragBox.style.left = nowLeft + "px";

            dragBox.style.top = nowTop + "px";

        }, false);

    }, false);

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

        dragBox.removeEventListener("touchstart,touchmove,touchend", function() {

        });

    }, false)

}, false);

//获取元素样式

function getCss(curEle, attr) {

    var val = null,

        reg = null;

    if ("getComputedStyle" in window) {

        val = window.getComputedStyle(curEle, null)[attr];

    } else {

        if (attr === "opacity") {

            val = curEle.currentStyle["filter"];

            reg = /^alpha\(opacity=(\d+(?:\.\d+)?)\)$/i;

            val = reg.test(val) ? reg.exec(val)[1] / 100 : 1;

        } else {

            val = curEle.currentStyle[attr];

        }

    }

    reg = /^(-?\d+(\.\d+)?)(px|pt|rem|em)?$/i;

    return reg.test(val) ? parseFloat(val) : val;

}