Good post and blog.

here's mine.

================== is server available? ===============================

var Available = function(onCallBack, offCallBack) { this.onCB = onCallBack; this.offCB = offCallBack;

this._worker = this.roll(); };

Available.prototype.roll = function() { return setInterval(this.bind(this.doCheck), "5000"); }

Available.prototype.regCallback = function(oncase, func) { if(oncase.toLowerCase == "online") this.onCB = func; else this.offCB = func; };

Available.prototype.discode = { 0: true, 500: true, 502: true, 503: true, 509: true };

Available.prototype._xhrCandidates = [ function() { return new XMLHttpRequest(); }, function() { return new ActiveXObject('Msxml2.XMLHTTP'); }, function() { return new ActiveXObject('Microsoft.XMLHTTP'); }, function() { return new ActiveXObject('Msxml2.XMLHTTP.4.0'); }, ];

Available.prototype.xhr = function() { if(!this.__xhr) { find_XMLHTTP: for(var i=0; i<this._xhrCandidates.length; i++) { try { this.__xhr = this._xhrCandidates[i](); break find_XMLHTTP; } catch(e) { } } }

return this.__xhr; };

Available.prototype.doCheck = function() { try { var url = location.protocol + "//" + location.hostname + "/" + new Date().getTime();

this.xhr().open('GET', url, false); this.xhr().send(null);

var callback = (this.xhr().status in this.discode) ? "offCB" : "onCB"; if(callback) this[callback](); } catch(e) { if(this._worker) clearInterval(this._worker); } };

Available.prototype.bind = function(func) { var scope = this; return function() { return func.apply(scope); } };

//=========== use ================

new Available( function() { // when on alert("online") }, function() { // when off alert("offline") } );

2008/2/2, dfalck <davi...@gmail.com>:

http://positionabsolute.net/blog/2007/09/google-gears-offline-detection.php