window["MzBrowser"] ={}; 
(function() 
{ 
if(MzBrowser.platform) return; 
var ua = window.navigator.userAgent; 
MzBrowser.platform = window.navigator.platform; 
MzBrowser.firefox = ua.indexOf("Firefox") > 0; 
MzBrowser.opera = typeof(window.opera) == "object"; 
MzBrowser.ie = ! MzBrowser.opera && ua.indexOf("MSIE") > 0; 
MzBrowser.mozilla = window.navigator.product == "Gecko"; 
MzBrowser.netscape = window.navigator.vendor == "Netscape"; 
MzBrowser.safari = ua.indexOf("Safari") > - 1; 
if(MzBrowser.firefox) var re = /Firefox(\s|\/)(\d+(\.\d+)?)/; 
else if(MzBrowser.ie) var re = /MSIE( )(\d+(\.\d+)?)/; 
else if(MzBrowser.opera) var re = /Opera(\s|\/)(\d+(\.\d+)?)/; 
else if(MzBrowser.netscape) var re = /Netscape(\s|\/)(\d+(\.\d+)?)/; 
else if(MzBrowser.safari) var re = /Version(\/)(\d+(\.\d+)?)/; 
else if(MzBrowser.mozilla) var re = /rv(\:)(\d+(\.\d+)?)/; 
if("undefined" != typeof(re) && re.test(ua)) 
MzBrowser.version = parseFloat(RegExp.$2); 
} 
)(); 
function upLoadKey(e, object) 
{ 
if((document.all) ? true : false) 
{ 
window.event.keyCode == 9 ? (window.event.returnValue = true) : (window.event.returnValue = false); 
} 
else 
{ 
if(object.value == "" && typeof e.which == "number")e.preventDefault(); 
if(object.value != "") object.blur(); 
} 
} 
function version(object) 
{ 
if(MzBrowser.firefox && MzBrowser.version == 2)object.blur(); 
} 
function clearValue(id) 
{ 
var up = (typeof id == "string") ? document.getElementById(id) : id; 
if (typeof up != "object") return null; 
var tt = document.createElement("span"); 
tt.id = "__tt__"; 
up.parentNode.insertBefore(tt, up); 
var tf = document.createElement("form"); 
tf.appendChild(up); 
document.getElementsByTagName("body")[0].appendChild(tf); 
tf.reset(); 
tt.parentNode.insertBefore(up, tt); 
tt.parentNode.removeChild(tt); 
tt = null; 
tf.parentNode.removeChild(tf); 
} 

// 頁面代碼

復(fù)制代碼代碼如下:

<html> 
<head> 
<script language="javascript" src="upLoad.js"></script> 
</head> 
<body> 
<input name="textfield3" type="file" class="input" id="textfield3" size="30" value="" ondrag="return false;" oncut="return false;" onkeydown="upLoadKey(event,this);" onpaste="return false;" onmousedown="document.oncontextmenu = function() { return false;}" onmouseout="document.oncontextmenu = function() { return true;};version(this);" tabIndex = -1/> <input type="button" id="clear" value="清 空" onclick="clearValue('textfield3');"/> 
</body> 
</html> 

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