JS judges whether the current browser is IE, and when it returns, what is IE?

Original reference:

https://www.cnblogs.com/liuyanxia/p/5855760.html

Specific code example:

What is returned here is: if not IE browser returns -1, returns 7/8/9/10/11 corresponding to the current IE version.

IEVersion();
 function IEVersion() {
     var userAgent = navigator.userAgent; // Get the browser's userAgent string   
    var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > - 1; // Determine whether IE<11 browser   
    var isEdge = userAgent.indexOf("Edge") > -1 && !isIE; // Determine whether IE's Edge browser   
    var isIE11 = userAgent.indexOf('Trident') > -1 && userAgent.indexOf("rv:11.0") > -1 ;
     if (isIE) {
         var reIE = new RegExp("MSIE (\\d+\\.\\d+);" );
        reIE.test(userAgent);
        var fIEVersion = parseFloat(RegExp["$1"]);
        if(fIEVersion == 7) {
            return 7;
        } else if(fIEVersion == 8) {
            return 8;
        } else if(fIEVersion == 9) {
            return 9;
        } else if(fIEVersion == 10) {
            return 10;
        } else {
             return 6; // IE version <=7 
        }   
    } else if(isEdge) {
        return 'edge';//edge
    } else if(isIE11) {
        return 11; //IE11  
    }else{
        return -1;//不是ie浏览器
    }
}