本文实例讲述了JavaScript使用面向对象实现的拖拽功能。分享给大家供大家参考，具体如下：
面向对象有个前提：
- 前提：所有东西都必须包含在onload里
- 改写：不能有函数嵌套，可以有全局变量
- 过程，如下
- onload改成构造函数，
- 全局变量改成属性（通过this）
- 函数改写成方法
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>面向对象的继承-1</title>
<style>
#div1 {width: 100px; height: 100px; background: red; position: absolute;}
</style>
<script>
window.onload = function() {
var oDiv = document.getElementById('div1');
oDiv.onmousedown = function(ev) {
var ev = ev || event;
var disX = ev.clientX - this.offsetLeft;
var disY = ev.clientY - this.offsetTop;
document.onmousemove = function(ev) {
var ev = ev || event;
oDiv.style.left = ev.clientX - disX + 'px';
oDiv.style.top = ev.clientY - disY + 'px';
}
document.onmouseup = function() {
document.onmousemove = document.onmouseup = null;
}
}
}
</script>
</head>
<body>
<div id="div1"></div>
</body>
</html>
把局部变量改成全局变量
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>面向对象的继承-2</title>
<style>
#div1 {width: 100px; height: 100px; background: red; position: absolute;}
</style>
<script>
var oDiv=null;
var disX=0;
var disY=0;
window.onload = function() {
oDiv = document.getElementById('div1');
oDiv.onmousedown = fnDown;
}
function fnMove(ev) {
var ev = ev || event;
oDiv.style.left = ev.clientX - disX + 'px';
oDiv.style.top = ev.clientY - disY + 'px';
}
function fnUp() {
document.onmousemove = document.onmouseup = null;
}
function fnDown(ev) {
var ev = ev || event;
disX = ev.clientX - this.offsetLeft;
disY = ev.clientY - this.offsetTop;
document.onmousemove = fnMove;
document.onmouseup =fnUp;
}
</script>
</head>
<body>
<div id="div1"></div>
</body>
</html>
引用块内容
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>面向对象的继承-2</title>
<style>
#div1 {width: 100px; height: 100px; background: red; position: absolute;}
#div2 {width: 100px; height: 100px; background: red; position: absolute;top:120px;}
</style>
<script>
window.onload=function(){
new Drag('div1');
new Drag('div2');
}
function Drag(id) {
var _this=this;
this.disX=0;
this.disY=0;
this.oDiv = document.getElementById(id);
this.oDiv.onmousedown = function(){
_this.fnDown()
};
}
Drag.prototype.fnDown=function (ev) {
var ev = ev || event;
var _this=this;
this.disX = ev.clientX - this.oDiv.offsetLeft;
this.disY = ev.clientY - this.oDiv.offsetTop;
document.onmousemove = function(){
_this.fnMove();
};
document.onmouseup =function(){
_this.fnUp();
};
}
Drag.prototype.fnMove=function(ev) {
var ev = ev || event;
this.oDiv.style.left = ev.clientX - this.disX + 'px';
this.oDiv.style.top = ev.clientY - this.disY + 'px';
}
Drag.prototype.fnUp=function () {
document.onmousemove = null;
document.onmouseup = null
}
</script>
</head>
<body>
<div id="div1"></div>
<div id="div2"></div>
</body>
</html>
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>面向对象的继承-2</title>
<style>
#div1 {width: 100px; height: 100px; background: red; position: absolute;}
#div2 {width: 100px; height: 100px; background: red; position: absolute;top:120px;}
</style>
<script>
window.onload=function(){
new Drag('div1');
new Drag('div2');
}
function Drag(id) {
var _this=this;
this.disX=0;
this.disY=0;
this.oDiv = document.getElementById(id);
this.oDiv.onmousedown = function(){
_this.fnDown()
};
}
Drag.prototype.fnDown=function (ev) {
var ev = ev || event;
var _this=this;
this.disX = ev.clientX - this.oDiv.offsetLeft;
this.disY = ev.clientY - this.oDiv.offsetTop;
document.onmousemove = function(){
_this.fnMove();
};
document.onmouseup =function(){
_this.fnUp();
};
}
Drag.prototype.fnMove=function(ev) {
var ev = ev || event;
this.oDiv.style.left = ev.clientX - this.disX + 'px';
this.oDiv.style.top = ev.clientY - this.disY + 'px';
}
Drag.prototype.fnUp=function () {
document.onmousemove = null;
document.onmouseup = null
}
</script>
</head>
<body>
<div id="div1"></div>
<div id="div2"></div>
</body>
</html>
感兴趣的朋友可以使用在线HTML/CSS/JavaScript代码运行工具：http://tools.jb51.net/code/HtmlJsRun测试一下运行效果。
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希望本文所述对大家JavaScript程序设计有所帮助。