JSFiddle - React, Tailwind, and code Playground

JavaScript

var nVer = navigator.appVersion;
    var nAgt = navigator.userAgent;
    var browserName  = navigator.appName;
    var fullVersion  = ''+parseFloat(navigator.appVersion); 
    var majorVersion = parseInt(navigator.appVersion,10); // this is what you need
    var nameOffset,verOffset,ix;
    
   
    // In Firefox, the true version is after "Firefox" 
    if ((verOffset=nAgt.indexOf("Firefox"))!=-1) {
     browserName = "Firefox";
     fullVersion = nAgt.substring(verOffset+8);
    }
    // In most other browsers, "name/version" is at the end of userAgent 
    else if ( (nameOffset=nAgt.lastIndexOf(' ')+1) < 
              (verOffset=nAgt.lastIndexOf('/')) ) 
    {
     browserName = nAgt.substring(nameOffset,verOffset);
     fullVersion = nAgt.substring(verOffset+1);
     if (browserName.toLowerCase()==browserName.toUpperCase()) {
      browserName = navigator.appName;
     }
    }
    // trim the fullVersion string at semicolon/space if present
    if ((ix=fullVersion.indexOf(";"))!=-1)
       fullVersion=fullVersion.substring(0,ix);
    if ((ix=fullVersion.indexOf(" "))!=-1)
       fullVersion=fullVersion.substring(0,ix);
    
    majorVersion = parseInt(''+fullVersion,10);
    if (isNaN(majorVersion)) {
     fullVersion  = ''+parseFloat(navigator.appVersion); 
     majorVersion = parseInt(navigator.appVersion,10);
    }
    
    console.log(''
     +'Browser name  = '+browserName+'<br>'
     +'Full version  = '+fullVersion+'<br>'
     +'Major version = '+majorVersion+'<br>'
     +'navigator.appName = '+navigator.appName+'<br>'
     +'navigator.userAgent = '+navigator.userAgent+'<br>');