原生js實現拖拽效果

面向對象 + 原生js拖拽

拖拽div等盒子模型，都是日常操作沒有什么問題，如果是拖拽圖片的話，會有一點小坑要踩......

那么我們看代碼:

``` var Move_fn = {}; (function(Move_fn){ function Move_img() {

}
Move_img.prototype = {
	constructor:Move_img,
	pageInit: function(imgEle, imgContent) {
		this.Ele = imgEle;
		this.Box = imgContent;
                    imgEle.className = "_positon";//添加定位屬性便於計算拖拽位置
		this._mw = imgContent.offsetWidth - imgEle.offsetWidth;
		this._mh = imgContent.offsetHeight - imgEle.offsetHeight;
		this.mouseDown();
		this.closeEvt();
	},
	closeEvt:function() {
		var that = this;
		this.Box.onclick = function(e) {
			e.preventDefault();
			e.stopPropagation();
			if(e.target.tagName == "DIV" || e.srcElement.tagName == "div") {
				Elf.utils.remove(that.Box.parentNode, that.Box.parentNode.parentNode);
			}
		}
	},
	mouseDown: function() {
		var that = this;
		this.Ele.onmousedown = function(e) {
			that.offX = e.offsetX;
			that.offY = e.offsetY;
			that.mouseMove();
		}
	},
	mouseMove: function(){
		var that = this;
		document.onmousemove = function(e) {
			var l = e.clientX - that.offX;
			var t = e.clientY - that.offY;
			//判斷邊界設置最大最小值
			if(t <= 0) {
				t = 0;
			}
			if(t >= that._mh) {
				t = that._mh;
			}
			if(l <= 0) {
				l = 0;
			}
			if(l >= that._mw) {
				l = that._mw;
			}
			that.Ele.style.top = t + "px";
			that.Ele.style.left = l + "px";
			that.mouseUp();
		}
	},
	mouseUp: function() {
		var that = this;
		document.onmouseup = function(e) {
			document.onmousemove = null;
			document.onmousedown = null;
		}
	}
}
Move_fn.move_img = new Move_img();

}(Move_fn));

<p>使用方式也橫簡單，Move_fn.move_img.pageInit(imgShow, imgContent);初始化一下就好了。要求imgContent全屏遮蓋</p>
<p>現在來說一下，圖片拖拽的小坑。當鼠標移動到圖片上的時候，會有一個，圖片選中可拖拽的狀態，這個時候我們執行的是ondragstart、draggable事件，而不是自行添加的onmousemove事件。會造成的后果是什么呢？拖拽后圖片卡頓，自行添加的鼠標抬起事件onmouseup失效，當我們的鼠標抬起后依然會執行鼠標移動事件，即鼠標抬起后圖片會跟着鼠標跑</p>
![](https://images2018.cnblogs.com/blog/1244681/201809/1244681-20180903161715077-1922354997.png)

<p>解決辦法：禁止掉圖片自己的拖拽事件<br />
對要拖拽的圖片添加幾個屬性
<ul>
	<li>oncontextmenu:"false"&nbsp;&nbsp;&nbsp;&nbsp;<span>禁止圖片右鍵菜單彈出</span></li>
	<li>onselectstart:"false"&nbsp;&nbsp;&nbsp;&nbsp;<span>禁止圖片選中</span></li>
	<li>ondragstart:"false"&nbsp;&nbsp;&nbsp;&nbsp;<span>禁止圖片拖拽</span></li>
	<li>draggable:"false"&nbsp;&nbsp;&nbsp;&nbsp;<span>禁止圖片拖拽</span></li>
</ul>
</p>