What are the steps to resolve TypeScript errors in OpenLayers version 6.6.1?

Since updating to OpenLayers 6.6.1, I have been bombarded with numerous typescript errors related to generics.

For example...

import olLayerVector from 'ol/layer/Vector';
import olFeature from 'ol/Feature';

public static highlightOverlay: olLayerVector = new olLayerVector({});
const selectedFeatures: Array<olFeature> = 
MapValues.highlightOverlay.getSource().getFeatures();

this code snippet is causing the following errors:

Generic type 'VectorLayer' requires 1 type argument(s)

Generic type 'Feature' requires 1 type argument(s).

I've come across some discussions like...

https://github.com/openlayers/openlayers/issues/8673

which suggest that using // @ts-ignore might be a workaround, but I'm looking for a better solution than cluttering my project with typescript errors related to generics.

If anyone has any insights or solutions, I would greatly appreciate your help.

typescriptopenlayersopenlayers-6angular-openlayers

Answer №1

After performing a major upgrade on a substantial angular project, I made the switch to OpenLayers 6.6.1 and opted for using the OpenLayers generated typescript declaration files over the @types/ol declaration files.

Utilizing generics in both Feature and VectorLayer, the former for the Geometry type and the latter for the source type, proved to be crucial in avoiding 'Generic type 'Foo' requires 1 type argument(s)' errors. By incorporating generics directly into the code as shown below, these issues were mitigated:

import { Feature } from 'ol';
import { Geometry } from 'ol/geom';
import { Vector } from 'ol/layer';
import { Vector as VectorSource } from 'ol/source';

// Typescript complains:
let f1: Feature = new Feature();
let vl1: Vector = new Vector({});

// Typescript is fine
let f2: Feature<Geometry> = new Feature<Geometry>();
let vl2: Vector<VectorSource<Geometry>> = new Vector<VectorSource<Geometry>>({});

The need for a generic in VectorSource relating to its geometry type explains the requirement for 

Vector<VectorSource<Geometry>>
in the code.

Since there was no necessity for type safety concerning the Geometry type, the superclass Geometry sufficed. However, if the Feature and source exclusively contained Point geometry features, one could replace Geometry with something like Point.

The older @types/ol declarations had defaults for the generics which eliminated the need for this syntax.

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