找不到名称“Drag”。请问这个问题是因为Drag这个类没有继承过来吗

Question

function LimitDrag(id) {
    Drag.call(this, id);    //继承属性
}
for (var i in Drag.prototype) {  //继承方法
    LimitDrag.prototype[i] = Drag.prototype[i];
}
LimitDrag.prototype.fnMove = function (ev) {
    var oEvent = ev || event;
    var l = oEvent.clientX - this.disX;
    var t = oEvent.clientY - this.disY;
    if (l < 0) {
        l = 0;
    } else if (l > document.documentElement.clientWidth - this.oDiv.offsetWidth) {
        l = document.documentElement.clientWidth - this.oDiv.offsetWidth;
    }

    if ( t< 0) {
         t= 0;
    } else if (t > document.documentElement.clientHeight - this.oDiv.offsetHeight) {
        t = document.documentElement.clientHeight - this.oDiv.offsetHeight;
    }
     
    this.oDiv.style.left = l + 'px';
    this.oDiv.style.top = t + 'px';

Answer 1

但是页面功能还是正常的