移动端滑块拖动

var div1 = document.querySelector('#kefu');
//限制最大宽高，不让滑块出去
var maxW = document.body.clientWidth - div1.offsetWidth;
var maxH = document.body.clientHeight - div1.offsetHeight;
 
//手指触摸开始，记录div的初始位置
div1.addEventListener('touchstart', function(e) {
    var ev = e || window.event;
    var touch = ev.targetTouches[0];
    oL = touch.clientX - div1.offsetLeft;
    oT = touch.clientY - div1.offsetTop;
    document.addEventListener("touchmove", defaultEvent, false);
});
//触摸中的，位置记录
div1.addEventListener('touchmove', function(e) {
    var ev = e || window.event;
    var touch = ev.targetTouches[0];
    var oLeft = touch.clientX - oL;
    var oTop = touch.clientY - oT;
    if(oLeft < 0) {
        oLeft = 0;
    } else if(oLeft >= maxW) {
        oLeft = maxW;
    }
    if(oTop < 0) {
        oTop = 0;
    } else if(oTop >= maxH) {
        oTop = maxH;
    }
 
    div1.style.left = oLeft + 'px';
    div1.style.top = oTop + 'px';
 
});
//触摸结束时的处理
div1.addEventListener('touchend', function() {
    document.removeEventListener("touchmove", defaultEvent);
});
 
//阻止默认事件
function defaultEvent(e) {
    e.preventDefault();
}