javascript完美拖拽的实现方法_javascript技巧

HTML代码：

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用户名：

密　码：

CSS代码：

body, h2 {
margin:0;
padding:0;
}
#login {
width:350px;
height:250px;
border:1px solid #ccc;
position:absolute;
left:512px;
top:300px;
}
#login h2 {
font-size:14px;
text-align:center;
height:30px;
line-height:30px;
background:#f60;
color:white;
cursor:move;
margin-bottom:30px;
letter-spacing:1px;
}
#login .user, #login .pass {
text-align:center;
font-size:12px;
height:60px;
line-height:40px;
}
#login .txt {
width:200px;
border:1px solid #ccc;
background:#fff;
height:30px;
line-height:30px;
}
#login .submit {
text-align:right;
}
#login .button {
width:100px;
height:30px;
background:#06f;
border:none;
cursor:pointer;
margin:10px 30px;
color:white;
letter-spacing:1px;
font-weight:bold;
}

拖拽核心代码：

function drag(obj) {
if (typeof obj === 'string') {
var obj = document.getElementById(obj);
} else {
var obj = obj;
}
function fixEvent(event) {
event.target = event.srcElement;
event.preventDefault = fixEvent.preventDefault;
return event;
}
fixEvent.preventDefault = function () {
this.returnValue = false;
};
obj.onmousedown = mousedown;
function mousedown(e) {
var e = e || fixEvent(window.event);
var disX = e.clientX - obj.offsetLeft;
var disY = e.clientY - obj.offsetTop;
if (e.target.tagName === 'H2') {
document.onmousemove = move;
document.onmouseup = up;
} else {
document.onmousemove = null;
document.onmouseup = null;
}
function move(e) {
var e = e || fixEvent(window.event);
var left = e.clientX - disX;
var top = e.clientY - disY;
if (obj.setCapture) {
obj.setCapture();
}
if (left left = 0;
} else if (left > document.documentElement.clientWidth - obj.offsetWidth) {
left = document.documentElement.clientWidth - obj.offsetWidth;
}
if (top top = 0;
} else if (top > document.documentElement.clientHeight - obj.offsetHeight) {
top = document.documentElement.clientHeight - obj.offsetHeight;
}
obj.style.left = left + 'px';
obj.style.top = top + 'px';
return false;
};
function up() {
if (obj.releaseCapture) {
obj.releaseCapture();
}
document.onmousemove = null;
document.onmouseup = null;
}
};
}

调用代码：

window.onload = function () {
var login = document.getElementById('login');
drag(login);
};

欢迎批评指正！！！