this is bound to functions, need to make that a arrow function

[oehm-smith]

This code fails:

if (Array.isArray(objects)) {
      geojson = { type: "FeatureCollection", features: [] };
      objects.forEach(function(item) {
        geojson.features.push(
          this.getFeature({ item: item, params: settings, propFunc: propFunc })
        );
      });
      this.addOptionals(geojson, settings);
    } else {
      geojson = this.getFeature({

this inside functions is bound to the function.

It needs to rewritten with arrow function so that this is bound to the original object:

    if (Array.isArray(objects)) {
      geojson = { type: "FeatureCollection", features: [] };
      objects.forEach((item) => {
        geojson.features.push(
          this.getFeature({ item: item, params: settings, propFunc: propFunc })
        );
      });
      this.addOptionals(geojson, settings);
    } else {

It's also good to use let or const instead of var since the latter has global scope.

Thanks for writing this as I too struck the problem of the geojson .js project not having @types. I think the better path would have been to insist https://github.com/caseycesari/GeoJSON.js rename their project and create a .dt. You seem to know them and perhaps you could have this conversation? :)

[eugeneYWang]

Thank you for this suggestion! I would find sometime to solve this.

Casey the original author have not been active in that repo for quote some years. I don't know if she would like to spend time to work with those orgs to change its name.

[eugeneYWang]

I wonder if you have tested this change in your own project?

It looks great but since it worked with me before I am wondering why it cause your concern here.

[echelon35]

Hi, I had the same problem.
I tried to make a FeatureGroup with multiple LineString.
I had this error :
Cannot read properties of undefined (reading 'getFeature')

I've just add this context inside the foreach loop because it was not bound to the original object :
//Line 58 of geojson.ts
objects.forEach(function(item) { geojson.features.push( this.getFeature({ item: item, params: settings, propFunc: propFunc }) ); }, this);

It works fine now :
{ "type": "FeatureCollection", "features": [ { "type": "Feature", "geometry": { "type": "LineString", "coordinates": [ [ -34.7, 10.5 ], [ -36.1, 11 ] ] }, "properties": { "type": "LineString" } }, ...