ie浏览器探测

//方式一
var isIE=!!window.ActiveXObject;
var isIE6=isIE&&!window.XMLHttpRequest;
var isIE8=isIE&&!!document.documentMode;
var isIE7=isIE&&!isIE6&&!isIE8;
if (isIE){
	if (isIE6){
		alert('ie6');
	}else if (isIE8){
		alert('ie8');
	}else if (isIE7){
		alert('ie7');
	}
};
//方式二
if(navigator.appName == 'Microsoft Internet Explorer' && navigator.appVersion.match(/6./i)=='6.'){ 
	alert('IE 6'); 
} 
else if(navigator.appName == 'Microsoft Internet Explorer' && navigator.appVersion.match(/7./i)=='7.'){ 
	alert('IE 7'); 
} 
else if(navigator.appName == 'Microsoft Internet Explorer' && navigator.appVersion.match(/8./i)=='8.'){ 
	alert('IE 8'); 
} 
else if(navigator.appName == 'Microsoft Internet Explorer' && navigator.appVersion.match(/9./i)=='9.'){ 
	alert('IE 9'); 
};
//方式三
if(navigator.userAgent.indexOf('Opera') != -1) { 
	alert('Opera'); 
} 
else if(navigator.userAgent.indexOf('MSIE') != -1) { 
	alert('Internet Explorer'); 
} 
else if(navigator.userAgent.indexOf('Firefox') != -1) { 
	alert('Firefox'); 
} 
else if(navigator.userAgent.indexOf('Netscape') != -1) { 
	alert('Netscape'); 
} 
else if(navigator.userAgent.indexOf('Safari') != -1) { 
	alert('Safari'); 
} 
else{ 
	alert('无法识别的浏览器。'); 
};
//方式四
if(!+'\v1' && !'1'[0]){ 
	alert('ie6或ie7') 
}