How does JS judge the browser type and distinguish the browsers of each version of IE in detail

Today, JS is used to judge the browser type, so the system has been sorted out for later use.

 /* 
  *  Description: Determine browser information  
  *  Prepare: LittleQiang_w 
  *  Date: 2016.1.5 
  *  Version: V1.1 
  */ 
 
 // Determine the current browsing type  
 function BrowserType() 
 { 
   var userAgent = navigator.userAgent; // Object of the browser userAgent String  
   var isOpera = userAgent.indexOf("Opera") > -1; // Judge whether Opera Browser  
   var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera; // Judge whether IE Browser  
   var isEdge = userAgent.indexOf("Windows NT 6.1; Trident/7.0;") > -1 && !isIE; // Judge whether IE Adj. Edge Browser  
   var isFF = userAgent.indexOf("Firefox") > -1; // Judge whether Firefox Browser  
   var isSafari = userAgent.indexOf("Safari") > -1 && userAgent.indexOf("Chrome") == -1; // Judge whether Safari Browser  
   var isChrome = userAgent.indexOf("Chrome") > -1 && userAgent.indexOf("Safari") > -1; // Judge Chrome Browser  
 
   if (isIE)  
   { 
      var reIE = new RegExp("MSIE (\\d+\\.\\d+);"); 
      reIE.test(userAgent); 
      var fIEVersion = parseFloat(RegExp["$1"]); 
      if(fIEVersion == 7) 
      { return "IE7";} 
      else if(fIEVersion == 8) 
      { return "IE8";} 
      else if(fIEVersion == 9) 
      { return "IE9";} 
      else if(fIEVersion == 10) 
      { return "IE10";} 
      else if(fIEVersion == 11) 
      { return "IE11";} 
      else 
      { return "0"}//IE The version is too low  
    }//isIE end 
     
    if (isFF) { return "FF";} 
    if (isOpera) { return "Opera";} 
    if (isSafari) { return "Safari";} 
    if (isChrome) { return "Chrome";} 
    if (isEdge) { return "Edge";} 
  }//myBrowser() end 
   
  // Determine whether it is IE Browser  
  function isIE() 
  { 
   var userAgent = navigator.userAgent; // Object of the browser userAgent String  
   var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera; // Judge whether IE Browser  
   if(isIE) 
   { 
     return "1"; 
   } 
   else 
   { 
     return "-1"; 
   } 
  } 
   
   
  // Determine whether it is IE Browser, including Edge Browser  
  function IEVersion() 
  { 
   var userAgent = navigator.userAgent; // Object of the browser userAgent String  
   var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera; // Judge whether IE Browser  
var isEdge = userAgent.indexOf("Windows NT 6.1; Trident/7.0;") > -1 && !isIE; // Judge whether IE Adj. Edge Browser  
   if(isIE) 
   { 
      var reIE = new RegExp("MSIE (\\d+\\.\\d+);"); 
      reIE.test(userAgent); 
      var fIEVersion = parseFloat(RegExp["$1"]); 
      if(fIEVersion == 7) 
      { return "IE7";} 
      else if(fIEVersion == 8) 
      { return "IE8";} 
      else if(fIEVersion == 9) 
      { return "IE9";} 
      else if(fIEVersion == 10) 
      { return "IE10";} 
      else if(fIEVersion == 11) 
      { return "IE11";} 
      else 
      { return "0"}//IE The version is too low  
   } 
else if(isEdge) 
{ 
  return "Edge"; 
} 
   else 
   { 
     return "-1";// Non IE 
   } 
  } 

The above code has passed the test and is available!

However, there is a problem, that is, IE5 and IE7 browsers cannot be distinguished for the time being. The following is the information of userAgent under IE5 and IE7; Through userAgent, it is found that IE5 and IE7 cannot be correctly distinguished simply by the above methods. Looking forward to the solution of this problem! ! !

IE5: userAgent "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/7.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; InfoPath.2; .NET4.0E)"

IE7: userAgent "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/7.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; InfoPath.2; .NET4.0E)"