javascript - browser detection

// Browser detection

// Internet Explorer
var ie  = document.all != null;  //ie4 and above
var ie5 = document.getElementById && document.all;
var ie6 = document.getElementById && document.all&&(navigator.appVersion.indexOf("MSIE 6.")>=0);

// Netscape
var ns4 = document.layers != null;
var ns6 = document.getElementById && !document.all;
var ns  = ns4 || ns6;

// Firefox
var ff  = !document.layers && !document.all;

// Opera
var op  = navigator.userAgent.indexOf("opera")>0;
var op7 = op && operaVersion() <= 7;
var op8 = op && operaVersion() >= 8;

// Detects the Opera version
function operaVersion() {
    agent = navigator.userAgent;
    idx = agent.indexOf("opera");
    if (idx>-1) {
        return parseInt(agent.subString(idx+6,idx+7));
    }
}