Detecting at the client Javascript browser type and version of Navigator is to use an object, and determine the current version of the browser vendor code parity typically sit sniffer browser (browser sniffer) sniffer or client (client sniffer) . In the early Web, and when both Netscape and IE platforms are not compatible when sniffing client (client sniffing) is a common client-side programming technology, and now the situation is basically stable compatibility, unlike a number of browser sniffing so common years ago, but occasionally some scenes will be used.
It should be noted that the client sniffer can also be done on the server side, Web server based on User-Agent header can optionally return a specific Javascript code to the client.