How to switch base layer based on internet connection availability

Question

My application ( html+ JavaScript) use Google map as a base layer. I also setup OSM as an offline base layer to use when there is no internet connection.

Now I'm locking for a way to make app check for internet connection, if there is, then use Google map as a base layer. if not, then use OSM.

Answer 1

You can listen for 'loaderror' event, that will be thrown, when loading of Google Map tile fails. Here is example with regular WMS layer (full example in http://jsfiddle.net/D3Eha/2/)

var wmsLayer, workingOffline = false;

wmsLayer = new OpenLayers.Layer.WMS("OpenLayers WMS",
    "http://vmap0.tiles.osgeo.org/wms/vmap0?",
    {layers: 'basic'},
    {
        attribution: 'Provided by OSGeo',
        tileOptions: {
            eventListeners: {
                'loaderror': function(evt) {
                    if (workingOffline == false) {
                        console.log('Tile load error, switching to offline map');
                        workingOffline = true;
                    }
                }
            }
        }        
    }
);

It's trickier to detect, when computer is online again. For example, when you go offline, start periodical timer to load some image from Internet. If it succeeds, you are back online.