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Native javascript implementation drag element sample code

  • 2020-03-30 03:48:14
  • OfStack

This article describes the native javascript implementation of element dragging.

Ideas:

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, the drag is terminated.

At the same time, the encapsulation of the code and browser compatibility 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 = { 

//Initialize the
initialize : function (element, options) { 

this.element = this.$(element); //The object being dragged
this._x = this._y = 0; //The position of the mouse in the element
this._moveDrag = this.bind(this, this.moveDrag); 
this._stopDrag = this.bind(this, this.stopDrag); 

//Set the parameters
this.setOptions(options); 

//Set the mouse to "drag" the "handle" object (note the difference between the object being dragged)
this.handle = this.$(this.options.handle); 

//Set the callback function
this.onStart = this.options.onStart; 
this.onMove = this.options.onMove; 
this.onStop = this.options.onStop; 

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

this.changeLayout(); 

//Register to start dragging events
this.addHandler(this.handle, "mousedown", this.bind(this, this.startDrag)); 
}, 

//Changes the layout properties of the dragged object
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, //The event object
onStart : function () {}, //The callback function starts
onMove : function(){}, //Drag-and-drop callback function
onStop : function(){} //Callbacks when stopped
}; 
for(var p in options){ 
this.options[p] = options[p]; 
} 
}, 
$ : function (id) { 
return typeof id === "string" ? 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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