js determine browser version

The following is not considered judgment of IE9 browser

function getBrowserType () {
     var userAgent = the navigator.userAgent; // made browser userAgent string 
    var Browser = 'Unknown' ;
     IF (! useragent.indexOf ( "IEs") = -. 1 ) {
        browser="IE";
    }else if(userAgent.indexOf('Firefox')!=-1){
        browser="Firefox";
    }else if(userAgent.indexOf('OPR')!=-1){
        browser="Opera";
    }else if(userAgent.indexOf('Chrome')!=-1){
        browser="Chrome";
    }else if(userAgent.indexOf('Safari')!=-1){
        browser="Safari";
    }else if(userAgent.indexOf('Trident')!=-1){
        browser='IE 11';
    }
    return browser;
}

test