User console redirection webpage uses unnecessary browser sniffing

Question

User console redirection webpage uses unnecessary browser sniffing
https://ps.palmws.com/palmcsext/console/
That user console redirection webpage has this piece of JavaScript that uses unnecessary browser sniffing:
<script type="text/javascript" language="javascript">
function checkBrowser()
var agt=navigator.userAgent.toLowerCase();
var is_mac = (agt.indexOf("mac")!=-1);
var is_ie = (agt.indexOf("msie")!= -1);
var is_opera = (agt.indexOf("opera")!= -1);
var is_firefox = (agt.indexOf("firefox")!= -1);
var is_window = (agt.indexOf("window")!= -1);
var is_safari = (agt.indexOf("safari")!= -1);
if (is_window) {
if (is_firefox || is_ie || is_safari) {
window.location = "/palmcsext/console/pages/LoginPage.iface";
} else {
window.location = "/palmcsext/console/notfound/notfound.html";
} else if (is_mac) {
window.location = "/palmcsext/console/pages/LoginPage.iface";
} else {
window.location = "/palmcsext/console/pages/LoginPage.iface";
</script>
The browser sniffing is pretty harmful. Remove it.
Just simply change the script to:
window.location = "/palmcsext/console/pages/LoginPage.iface";

Answer 1

XP1 wrote:
If you look at the logic, even unsupported browsers will pass the test.
The if statements only check for supported browsers running on Windows or Mac OSes. If the user is using a different OS, regardless of supported or unsupported browser, the webpage will still redirect correctly.
The script doesn't do a good job of checking for supported browsers either. The user can set a custom user agent, and the code can't rely on the user agent string.
Checking for browser support should be done by feature detection, not by user agent string checking.
If the user sets a custom user agent string or uses a browser with which the code works, then it harms the user.
The concept of the web is that it should work everywhere. Blocking browsers not only harms the user but also harms the web.
If the code is written to web standards, the webpage should work in all modern browsers.
Thus, it is pointless, inefficient, and unnecessary to have those if statements there.
Like I said, the code can be simplified by just using 1 line:
window.location = "/palmcsext/console/pages/LoginPage.iface";
I have asked for more specifics here to find out why that logic is in place.  Not saying I can post back anything, but I have asked.
And unless I'm reading it wrong, the check for unsupported browsers (so anything NOT firefox, ie or safari) only happens if you're running windows.  If you're on Mac or some other OS, it directs to the working page.  I have asked about that, too.