JS代码判断IE6,IE7,IE8,IE9！

有一种代码：

<script type="text/javascript"> 
var browser=navigator.appName 
var b_version=navigator.appVersion 
var version=b_version.split(";"); 
var trim_Version=version[1].replace(/[ ]/g,""); 
if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE6.0") 
{ 
alert("IE 6.0"); 
} 
else if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE7.0") 
{ 
alert("IE 7.0"); 
} 
else if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE8.0") 
{ 
alert("IE 8.0"); 
} 
else if(browser=="Microsoft Internet Explorer" && trim_Version=="MSIE9.0") 
{ 
alert("IE 9.0"); 
} 
</script>

第二种：

<script type="text/javascript"> 
if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion .split(";")[1].replace(/[ ]/g,"")=="MSIE6.0") 
{ 
alert("IE 6.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion .split(";")[1].replace(/[ ]/g,"")=="MSIE7.0") 
{ 
alert("IE 7.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion .split(";")[1].replace(/[ ]/g,"")=="MSIE8.0") 
{ 
alert("IE 8.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion .split(";")[1].replace(/[ ]/g,"")=="MSIE9.0") 
{ 
alert("IE 9.0"); 
} 
</script>

第三种：

<script type="text/javascript"> 
if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion.match(/7./i)=="7.") 
{ 
alert("IE 7.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion.match(/8./i)=="8.") 
{ 
alert("IE 8.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion.match(/9./i)=="9.") 
{ 
alert("IE 9.0"); 
} 
else if(navigator.appName == "Microsoft Internet Explorer") 
{ 
alert("IE 6.0"); 
} 
</script>