Native javascript implementation of drag element sample code

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May 16, 2016 pm 04:38 PM

Native js

This article introduces native javascript to implement element dragging.

Things:

1. First change the layout attribute of the dragged element, the key is "position:absolue";

2. Capture mouse events "mousedown", "mousemove", "mouseup";

3. When "mousedown" is triggered, record the relative position of the current mouse in the element, _x, _y;

4. Then handle the "mousemove" event and move the element by changing the top and left attributes of the element;

5. When the "mouseup" time is triggered, terminate dragging.

At the same time, the encapsulation of the code and the compatibility of the browser should be considered. The code is as follows:

<!DOCTYPE html> 
<html> 
<head> 
<title>draggable div</title> 
<style type="text/css"> 
body{ 
margin: 0; 
padding: 0; 
background-color: #fff; 
} 

#drag_div{ 
width: 150px; 
height: 150px; 
padding: 10px; 
margin: 10px; 
background-color: #66dd33; 
cursor: move; 
} 
</style> 
</head> 
</html> 
<body> 
<div id="drag_div"></div> 
</body> 
<script type="text/javascript"> 

function Drag () { 
this.initialize.apply(this, arguments); 
} 

Drag.prototype = { 

// 初始化 
initialize : function (element, options) { 

this.element = this.$(element); // 被拖动的对象 
this._x = this._y = 0; // 鼠标在元素中的位置 
this._moveDrag = this.bind(this, this.moveDrag); 
this._stopDrag = this.bind(this, this.stopDrag); 

// 设置参数 
this.setOptions(options); 

// 设置鼠标去“拖”的“柄”对象（注意与被拖动的对象区别） 
this.handle = this.$(this.options.handle); 

// 设置回调函数 
this.onStart = this.options.onStart; 
this.onMove = this.options.onMove; 
this.onStop = this.options.onStop; 

this.handle.style.cursor = "move"; 

this.changeLayout(); 

// 注册开始拖动事件 
this.addHandler(this.handle, "mousedown", this.bind(this, this.startDrag)); 
}, 

// 改变被拖动对象的布局属性 
changeLayout: function () { 
this.element.style.top = this.element.offsetTop + "px"; 
this.element.style.left = this.element.offsetLeft + "px"; 
this.element.style.position = "absolute"; 
this.element.style.margin = "0"; 
}, 

startDrag : function (event) { 
var event = event || window.event; 

this._x = event.clientX - this.element.offsetLeft; 
this._y = event.clientY - this.element.offsetTop; 

this.addHandler(document, "mousemove", this._moveDrag); 
this.addHandler(document, "mouseup", this._stopDrag); 

this.preventDefault(event); 

this.handle.setCapture && this.handle.setCapture(); 

this.onStart(); 
}, 
moveDrag : function (event) { 
var event = this.getEvent(event); 

var iTop = event.clientY - this._y; 
var iLeft = event.clientX - this._x; 

this.element.style.top = iTop + "px"; 
this.element.style.left = iLeft + "px"; 

this.onMove(); 
}, 
stopDrag : function () { 

this.removeHandler(document, "mousemove", this._moveDrag); 
this.removeHandler(document, "mouseup", this._stopDrag); 
this.handle.releaseCapture && this.handle.releaseCapture(); 

this.onStop() 

}, 
setOptions : function (options) { 
this.options = { 
handle: this.element, //事件对象 
onStart : function () {}, // 开始时回调函数 
onMove : function(){}, // 拖拽时回调函数 
onStop : function(){} // 停止时回调函数 
}; 
for(var p in options){ 
this.options[p] = options[p]; 
} 
}, 
$ : function (id) { 
return typeof id === "string" &#63; document.getElementById(id):id; 
}, 
addHandler : function (element, eventType, handler) { 
if(element.addEventListener){ 
return element.addEventListener(eventType, handler, false); 
}else{ 
return element.attachEvent("on"+eventType, handler); 
} 
}, 
removeHandler : function (element, eventType, handler) { 
if(element.removeEventListener){ 
return element.removeEventListener(eventType, handler, false); 
}else{ 
return element.detachEvent("on" + eventType, handler); 
} 
}, 
getEvent: function (event) { 
return event || window.event; 
}, 
preventDefault: function (event) { 
if(event.preventDefault){ 
event.preventDefault(); 
}else{ 
event.returnValue = false; 
} 
}, 
bind : function (obj, handler) { 
return function () { 
return handler.apply(obj, arguments); 
} 
} 
}; 

window.onload = function () { 
var drag_div = document.getElementById("drag_div"); 

var drag = new Drag(drag_div, {handle: drag_div}); 
} 

</script> 
</html>

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