Dynamically assign feature properties on L.marker popup interactions

Question

I have a Leaflet based map on which a user can click to create a marker. Then, if one clicks on the marker a popup is opening, where one can change text in a textarea, activate the camera of the mobile device and save all markers with feature properties into a geoJSON.

I initialize an empty L.featureGroup(), generate dynamic HTML popupContent inside an addMarker(e){} function and add all this data to an object, that is being created via .toGeoJSON(), where I can access feature.properties. Because it is overwritten each time, I have to write all properties into another array infoTextArray

Is there a efficent way to directly write a feature's properties on creation?

edit: to further specify my question:

I want to assign my geoJSON features properties when they're created. I tried something like:

let layerGroup = L.geoJSON([], {
pointToLayer: function (feature) {
    feature.properties.infoText='';
    feature.properties.imageURL='';
},
onEachFeature: function (feature) {
    feature.properties.infoText='';
    feature.properties.imageURL=''; 
}
}).addTo(map);

layerGroup.toGEOJSON() still returns an empty feature properties object. I'm guessing my functions aren't triggered, when a new features is added to the layer.

Answer 1

Leaflet's toGeoJSON() functionality works by using the .feature property of L.Layers (in your case, L.Markers) inside the L.GeoJSON group. Relevant code is here and here.

Therefore, you should populate a .feature property in your L.Markers when the markers are created and not sooner.

e.g.:

var layerGroup = L.geoJSON();

map.on('click', function(ev){
  var newMarker = L.marker(ev.latlng);
  newmarker.feature = { 
    type: 'Point', 
    properties: { infoText: '', imageURL: '' }, 
    geometry: undefined 
  };
  newMarker.addTo(layerGroup);
});

// ...later
layerGroup.toGeoJSON();

Right now, you're trying to populate such a property of the markers before the markers even exist. Your pointToLayer and onEachFeature are not running ever, because they run over each feature in the GeoJSON data when the L.GeoJSON is instantiated, but you're instantiating it with no data - therefore each of them runs a grand total of zero times.