我要通过Niklas Zakas的书。我正在谈论自定义事件,目前正在浏览此代码:
var DragDrop = function(){
var dragdrop = new EventTarget(),
dragging = null,
diffX = 0,
diffY = 0;
function handleEvent(event){
//get event and target
event = EventUtil.getEvent(event);
var target = EventUtil.getTarget(event);
//determine the type of event
switch(event.type){
case "mousedown":
if (target.className.indexOf("draggable") > -1){
dragging = target;
diffX = event.clientX - target.offsetLeft;
diffY = event.clientY - target.offsetTop;
dragdrop.fire({type:"dragstart", target: dragging, x: event.clientX, y: event.clientY});
}
break;
case "mousemove":
if (dragging !== null){
//assign location
dragging.style.left = (event.clientX - diffX) + "px";
dragging.style.top = (event.clientY - diffY) + "px";
//fire custom event
dragdrop.fire({type:"drag", target: dragging, x: event.clientX, y: event.clientY});
}
break;
case "mouseup":
dragdrop.fire({type:"dragend", target: dragging, x: event.clientX, y: event.clientY});
dragging = null;
break;
}
};
//public interface
dragdrop.enable = function(){
EventUtil.addHandler(document, "mousedown", handleEvent);
EventUtil.addHandler(document, "mousemove", handleEvent);
EventUtil.addHandler(document, "mouseup", handleEvent);
};
dragdrop.disable = function(){
EventUtil.removeHandler(document, "mousedown", handleEvent);
EventUtil.removeHandler(document, "mousemove", handleEvent);
EventUtil.removeHandler(document, "mouseup", handleEvent);
};
return dragdrop;
}();
DragDrop.enable();
DragDrop.addHandler("dragstart", function(event){
var status = document.getElementById("status");
status.innerHTML = "Started dragging " + event.target.id;
});
DragDrop.addHandler("drag", function(event){
var status = document.getElementById("status");
status.innerHTML += "<br>Dragged " + event.target.id + " to (" + event.x + "," + event.y + ")";
});
DragDrop.addHandler("dragend", function(event){
var status = document.getElementById("status");
status.innerHTML += "<br>Dropped " + event.target.id + " at (" + event.x + "," + event.y + ")";
});
我的问题是关于调用函数DragDrop.enable();
我不知道如何调用一个启用函数,该函数不是直接在DragDrop上定义的,而是在dragdrop bject上定义的(在DragDrop的顶部定义)。
感谢您提出任何建议或指出阅读..
答案 0 :(得分:0)
DrapDrop 变量被赋予了拖拉对象(由于返回语句),其具有属性enable()
所以要调用enable,只需DragDrop.enable()
答案 1 :(得分:0)
代码使用一个立即调用的函数表达式(IIFE)来设置闭包中保存的一些变量。
在作业开始时:
var DragDrop = function(){
大多数人会把它写成:
var DragDrop = (function(){
其中“(”表示将执行函数表达式并分配结果,而不是函数本身。
dragdrop 对象在此处创建:
var dragdrop = new EventTarget(),
和此处指定的属性:
//public interface
dragdrop.enable = function(){
...
};
dragdrop.disable = function(){
...
};
然后将返回将分配给 DragDrop 的对象(当前由 dragdrop 引用):
return dragdrop;
最后,空参数列表会导致函数表达式被删除:
}();
更常见的是:
}());
平衡额外的“(”之前建议。所以 DragDrop 现在引用返回的对象( EventTarget 的一个实例),它可以访问在IIFE(例如拖动, diffX , diffY )但其他功能没有。