Use union type for source state

src/ol/layer/Base.js

@@ -260,7 +260,7 @@ class BaseLayer extends BaseObject {
 
   /**
    * @abstract
-   * @return {import("../source/State.js").default} Source state.
+   * @return {import("../source/Source.js").State} Source state.
    */
   getSourceState() {
     return abstract();

src/ol/layer/Group.js

@@ -7,7 +7,6 @@ import CollectionEventType from '../CollectionEventType.js';
 import Event from '../events/Event.js';
 import EventType from '../events/EventType.js';
 import ObjectEventType from '../ObjectEventType.js';
-import SourceState from '../source/State.js';
 import {assert} from '../asserts.js';
 import {assign, clear} from '../obj.js';
 import {getIntersection} from '../extent.js';
@@ -343,10 +342,10 @@ class LayerGroup extends BaseLayer {
   }
 
   /**
-   * @return {import("../source/State.js").default} Source state.
+   * @return {import("../source/Source.js").State} Source state.
    */
   getSourceState() {
-    return SourceState.READY;
+    return 'ready';
   }
 }
 

src/ol/layer/Layer.js

@@ -5,7 +5,6 @@ import BaseLayer from './Base.js';
 import EventType from '../events/EventType.js';
 import LayerProperty from './Property.js';
 import RenderEventType from '../render/EventType.js';
-import SourceState from '../source/State.js';
 import {assert} from '../asserts.js';
 import {assign} from '../obj.js';
 import {listen, unlistenByKey} from '../events.js';
@@ -213,7 +212,7 @@ class Layer extends BaseLayer {
    */
   getSourceState() {
     const source = this.getSource();
-    return !source ? SourceState.UNDEFINED : source.getState();
+    return !source ? 'undefined' : source.getState();
   }
 
   /**

src/ol/layer/MapboxVector.js

@@ -4,7 +4,6 @@
 import BaseEvent from '../events/Event.js';
 import EventType from '../events/EventType.js';
 import MVT from '../format/MVT.js';
-import SourceState from '../source/State.js';
 import VectorTileLayer from '../layer/VectorTile.js';
 import VectorTileSource from '../source/VectorTile.js';
 import {applyBackground, applyStyle} from 'ol-mapbox-style';
@@ -144,7 +143,7 @@ class MapboxVectorLayer extends VectorTileLayer {
   constructor(options) {
     const declutter = 'declutter' in options ? options.declutter : true;
     const source = new VectorTileSource({
-      state: SourceState.LOADING,
+      state: 'loading',
       format: new MVT(),
     });
 
@@ -179,12 +178,12 @@ class MapboxVectorLayer extends VectorTileLayer {
       accessToken: this.accessToken,
     })
       .then(() => {
-        source.setState(SourceState.READY);
+        source.setState('ready');
       })
       .catch((error) => {
         this.dispatchEvent(new ErrorEvent(error));
         const source = this.getSource();
-        source.setState(SourceState.ERROR);
+        source.setState('error');
       });
     if (this.getBackground() === undefined) {
       applyBackground(this, options.styleUrl, {