browser detect javascript

1//gets the type of browser
2function detectBrowser() { 
3    if((navigator.userAgent.indexOf("Opera") || navigator.userAgent.indexOf('OPR')) != -1 ) {
4        return 'Opera';
5    } else if(navigator.userAgent.indexOf("Chrome") != -1 ) {
6        return 'Chrome';
7    } else if(navigator.userAgent.indexOf("Safari") != -1) {
8        return 'Safari';
9    } else if(navigator.userAgent.indexOf("Firefox") != -1 ){
10        return 'Firefox';
11    } else if((navigator.userAgent.indexOf("MSIE") != -1 ) || (!!document.documentMode == true )) {
12        return 'IE';//crap
13    } else {
14        return 'Unknown';
15    }
16}