Set Active Layer of Multi-layer Map - leaflet

Question

I have a Leaflet Map with 5 layers, each with multiple map points. From any of 5 separate pages a user can select to view all of the map points for any one of the map layers. The desired type is passed via a URL to the View_All page. The View_All page contains the Leaflet map with the five layers dynamically built for the layers and map points.
What I need is first to set the user desired map layer to be the active layer after the map is fully built. Further, I will need to access the layer control to determine when the user has selected another layer so the page heading can be updated to reflect the type of information being viewed.
Here is a link to a quasi finished page.
TIA for any assistance.
jdadwilson

Answer 1

Add a layer control to your map, and then listening on the baselayerchange event.
var overlayMaps = {
"Cemeteries": l1, //l1,l2,... Layergroups or GeoJSON Layer
"Churches": l2,
"Markers": l3,
"Schools": l4,
"Towns": l5,
};
var text = {
"Cemeteries": "Test Cemeteries",
"Churches": "Test Churches",
"Markers": "Test Markers",
"Schools": "Test Schools",
"Towns": "Test Towns",
}
mymap.addLayer(l3); //Acitve Layer from URL
L.DomUtil.get("textheaderid").innerHTML = text["Markers"];
L.control.layers(overlayMaps).addTo(mymap);
mymap.on('baselayerchange',function(e){
console.log(e)
var name = e.name;
var str = text[e.name];
console.log(str);
L.DomUtil.get("textheaderid").innerHTML = str;
})
Example: https://jsfiddle.net/falkedesign/q1kmtf93/