ideas to check browser is online

is-online.js

/*
   @dependencies
   jQuery
*/
(function( window, $, undefined ){
    var support = {
            onLine: undefined === typeof window.navigator.onLine,
            applicationCache: !!window.applicationCache
        },
        app = {
            eventOnline: function(){
                if( support.onLine ){
                    if( window.navigator.onLine === false ){
                        //we are okay, browser is offline
                        $( document )
                            .removeClass( "online" )
                            .addClass( "offline" );
                    }
                    else if( window.navigator.onLine === true ){
                        //in chrome 15 onLine === true if computer is connected to the internet
                        //in ff, onLine === false if browser is set to work offline, otherwise it's true
                        //so if browser supports applicationCache
                        if( support.applicationCache ){
                            //if browser support appCache, we 
                            //just update it and listening for events
                            window.applicationCache.update();
                        }
                        else{
                            app.fallbackAjax();
                        }
                    }
                }
            },
            appCacheReady:function(){
                //we don't give a fuck, whether appCache can be updated,
                //we are just happy, because browser is online
                $( document )
                    .removeClass( "offline appcache-error" )
                    .addClass( "online appcache-success" );
            },
            appCacheError: function(){
                $( document )
                    .removeClass( "online appcache-success" )
                    .addClass( "appcache-error" );
            },
            fallbackAjax: function(){
                $.ajax({
                    url: "appcache.manifest",
                    success: function(){
                        $( document )
                            .removeClass( "offline" )
                            .addClass( "online" );
                    },
                    error: function(){
                        $( document )
                            .removeClass( "online" )
                            .addClass( "offline" );
                    },
                    complete: function(){
                        _interval = setTimeout( app.fallbackAjax );
                    }
                });
            }
        
        }, _interval;
    
    
    $( window )
        .on( "online.connected offline.connected", app.eventOnline )
        .trigger( "online.connected" );
    if( support.applicationCache ){
        $( window.applicationCache )
            .bind( "updateready", app.appCacheReady )
            .bind( "error", app.appCacheError );
    
    }
})( window, jQuery );