When you are displaying geojson with leaflet overlays, onEachFeature is a function will be applied on each feature, e.g. a point or a polygon in a features collection.

I overwrote the onEachFeature with a cusmerized function, when this funtion is running, it get the information from current display/undisplay layer, and changes the global variable gDisplayLayersInfo accordingly.

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function overlayOnEachFeature(feature, layer){
    layer.on({
        // when a overlay is on display
        add: function (e) {
            // get information from the current layer
            var layerInfo = getLayerInfo(layer);
            // add the information to a global variable
            gDisplayLayersInfo.push('<br>' + layerInfo);
        },
        remove: function (e) {
            var layerInfo = getLayerInfo(layer);
            var listElement = '<br>' + layerInfo;
            for (var l in gDisplayLayersInfo){
                // if the information is in the global variable, delete the information
                if (listElement === gDisplayLayersInfo[l]){
                    gDisplayLayersInfo.splice(l,1);
                };
            };
        }
    });
}

Apply the cusmerized onEachFeature to the layer which will be added:

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//add geojson polygon to the map
var transportationLayer = new L.geoJSON(gTransportation, {
    style: transportationStyle,
    // overwrite the function
    onEachFeature: overlayOnEachFeature
});