元素JS拖动的实现

涉及到了几个位置的属性

offset   clientX cilentY 等

$(selector).on("mousedown",function (e){
    var x = e.clientX - $("#mod").offset().left;
    var y = e.clientY - $("#mod").offset().top;
    document.onmousemove = function (e) {
        $("#mod").css({"left": e.clientX - x + "px"});
        $("#mod").css({"top": e.clientY - y + "px"});
    }
    document.onmouseup = function () {
    document.onmousemove = null;
    }
})