diff --git a/changelog/upgrade-notes.md b/changelog/upgrade-notes.md
index 51010030fb..fb18563470 100644
--- a/changelog/upgrade-notes.md
+++ b/changelog/upgrade-notes.md
@@ -2,6 +2,10 @@
 
 ### Next version
 
+#### The `getUid` function returns string
+
+The `getUid` function from the `ol/util` module now returns a string instead of a number.
+
 #### Attributions are not collapsible for `ol/source/OSM`
 
 When a map contains a layer from a `ol/source/OSM` source, the `ol/control/Attribution` control will be shown with the `collapsible: false` behavior.
diff --git a/src/ol/PluggableMap.js b/src/ol/PluggableMap.js
index 0f231b3b49..1a6690038f 100644
--- a/src/ol/PluggableMap.js
+++ b/src/ol/PluggableMap.js
@@ -42,7 +42,7 @@ import {create as createTransform, apply as applyTransform} from './transform.js
  * @property {null|import("./extent.js").Extent} extent
  * @property {import("./coordinate.js").Coordinate} focus
  * @property {number} index
- * @property {Object<number, import("./layer/Layer.js").State>} layerStates
+ * @property {Object<string, import("./layer/Layer.js").State>} layerStates
  * @property {Array<import("./layer/Layer.js").State>} layerStatesArray
  * @property {import("./transform.js").Transform} pixelToCoordinateTransform
  * @property {Array<PostRenderFunction>} postRenderFunctions
@@ -1068,7 +1068,7 @@ class PluggableMap extends BaseObject {
     }
     const view = this.getView();
     if (view) {
-      this.viewport_.setAttribute('data-view', getUid(view).toString());
+      this.viewport_.setAttribute('data-view', getUid(view));
       this.viewPropertyListenerKey_ = listen(
         view, ObjectEventType.PROPERTYCHANGE,
         this.handleViewPropertyChanged_, this);
@@ -1304,8 +1304,7 @@ class PluggableMap extends BaseObject {
    * @param {import("./Feature.js").default} feature Feature.
    */
   skipFeature(feature) {
-    const featureUid = getUid(feature).toString();
-    this.skippedFeatureUids_[featureUid] = true;
+    this.skippedFeatureUids_[getUid(feature)] = true;
     this.render();
   }
 
@@ -1340,8 +1339,7 @@ class PluggableMap extends BaseObject {
    * @param {import("./Feature.js").default} feature Feature.
    */
   unskipFeature(feature) {
-    const featureUid = getUid(feature).toString();
-    delete this.skippedFeatureUids_[featureUid];
+    delete this.skippedFeatureUids_[getUid(feature)];
     this.render();
   }
 }
diff --git a/src/ol/Tile.js b/src/ol/Tile.js
index 1aa36a01ca..f7a9dc0e78 100644
--- a/src/ol/Tile.js
+++ b/src/ol/Tile.js
@@ -122,7 +122,7 @@ class Tile extends EventTarget {
     /**
      * Lookup of start times for rendering transitions.  If the start time is
      * equal to -1, the transition is complete.
-     * @type {Object<number, number>}
+     * @type {Object<string, number>}
      */
     this.transitionStarts_ = {};
 
@@ -244,7 +244,7 @@ class Tile extends EventTarget {
 
   /**
    * Get the alpha value for rendering.
-   * @param {number} id An id for the renderer.
+   * @param {string} id An id for the renderer.
    * @param {number} time The render frame time.
    * @return {number} A number between 0 and 1.
    */
@@ -272,7 +272,7 @@ class Tile extends EventTarget {
    * Determine if a tile is in an alpha transition.  A tile is considered in
    * transition if tile.getAlpha() has not yet been called or has been called
    * and returned 1.
-   * @param {number} id An id for the renderer.
+   * @param {string} id An id for the renderer.
    * @return {boolean} The tile is in transition.
    */
   inTransition(id) {
@@ -284,7 +284,7 @@ class Tile extends EventTarget {
 
   /**
    * Mark a transition as complete.
-   * @param {number} id An id for the renderer.
+   * @param {string} id An id for the renderer.
    */
   endTransition(id) {
     if (this.transition_) {
diff --git a/src/ol/VectorImageTile.js b/src/ol/VectorImageTile.js
index 60bb05303a..e4fd58ceb6 100644
--- a/src/ol/VectorImageTile.js
+++ b/src/ol/VectorImageTile.js
@@ -191,7 +191,7 @@ class VectorImageTile extends Tile {
    * @return {CanvasRenderingContext2D} The rendering context.
    */
   getContext(layer) {
-    const key = getUid(layer).toString();
+    const key = getUid(layer);
     if (!(key in this.context_)) {
       this.context_[key] = createCanvasContext2D();
     }
@@ -213,7 +213,7 @@ class VectorImageTile extends Tile {
    * @return {ReplayState} The replay state.
    */
   getReplayState(layer) {
-    const key = getUid(layer).toString();
+    const key = getUid(layer);
     if (!(key in this.replayState_)) {
       this.replayState_[key] = {
         dirty: false,
diff --git a/src/ol/interaction/Modify.js b/src/ol/interaction/Modify.js
index c4d6f05840..5ed11e3f1e 100644
--- a/src/ol/interaction/Modify.js
+++ b/src/ol/interaction/Modify.js
@@ -788,7 +788,7 @@ class Modify extends PointerInteraction {
       for (let i = 0, ii = segmentDataMatches.length; i < ii; ++i) {
         const segmentDataMatch = segmentDataMatches[i];
         const segment = segmentDataMatch.segment;
-        let uid = String(getUid(segmentDataMatch.feature));
+        let uid = getUid(segmentDataMatch.feature);
         const depth = segmentDataMatch.depth;
         if (depth) {
           uid += '-' + depth.join('-'); // separate feature components
@@ -1038,7 +1038,7 @@ class Modify extends PointerInteraction {
     for (i = dragSegments.length - 1; i >= 0; --i) {
       dragSegment = dragSegments[i];
       segmentData = dragSegment[0];
-      uid = String(getUid(segmentData.feature));
+      uid = getUid(segmentData.feature);
       if (segmentData.depth) {
         // separate feature components
         uid += '-' + segmentData.depth.join('-');
diff --git a/src/ol/interaction/Select.js b/src/ol/interaction/Select.js
index e713456eae..a68a65430e 100644
--- a/src/ol/interaction/Select.js
+++ b/src/ol/interaction/Select.js
@@ -250,7 +250,7 @@ class Select extends Interaction {
      * An association between selected feature (key)
      * and layer (value)
      * @private
-     * @type {Object<number, import("../layer/Layer.js").default>}
+     * @type {Object<string, import("../layer/Layer.js").default>}
      */
     this.featureLayerAssociation_ = {};
 
@@ -267,8 +267,7 @@ class Select extends Interaction {
    * @private
    */
   addFeatureLayerAssociation_(feature, layer) {
-    const key = getUid(feature);
-    this.featureLayerAssociation_[key] = layer;
+    this.featureLayerAssociation_[getUid(feature)] = layer;
   }
 
   /**
@@ -299,9 +298,8 @@ class Select extends Interaction {
    * @api
    */
   getLayer(feature) {
-    const key = getUid(feature);
     return (
-      /** @type {VectorLayer} */ (this.featureLayerAssociation_[key])
+      /** @type {VectorLayer} */ (this.featureLayerAssociation_[getUid(feature)])
     );
   }
 
@@ -372,8 +370,7 @@ class Select extends Interaction {
    * @private
    */
   removeFeatureLayerAssociation_(feature) {
-    const key = getUid(feature);
-    delete this.featureLayerAssociation_[key];
+    delete this.featureLayerAssociation_[getUid(feature)];
   }
 }
 
diff --git a/src/ol/interaction/Snap.js b/src/ol/interaction/Snap.js
index 66f3d2ef15..944f18387a 100644
--- a/src/ol/interaction/Snap.js
+++ b/src/ol/interaction/Snap.js
@@ -127,7 +127,7 @@ class Snap extends PointerInteraction {
     this.featuresListenerKeys_ = [];
 
     /**
-     * @type {Object<number, import("../events.js").EventsKey>}
+     * @type {Object<string, import("../events.js").EventsKey>}
      * @private
      */
     this.featureChangeListenerKeys_ = {};
@@ -135,7 +135,7 @@ class Snap extends PointerInteraction {
     /**
      * Extents are preserved so indexed segment can be quickly removed
      * when its feature geometry changes
-     * @type {Object<number, import("../extent.js").Extent>}
+     * @type {Object<string, import("../extent.js").Extent>}
      * @private
      */
     this.indexedFeaturesExtents_ = {};
@@ -144,7 +144,7 @@ class Snap extends PointerInteraction {
      * If a feature geometry changes while a pointer drag|move event occurs, the
      * feature doesn't get updated right away.  It will be at the next 'pointerup'
      * event fired.
-     * @type {!Object<number, import("../Feature.js").default>}
+     * @type {!Object<string, import("../Feature.js").default>}
      * @private
      */
     this.pendingFeatures_ = {};
diff --git a/src/ol/layer/Group.js b/src/ol/layer/Group.js
index d910f27b80..ce765b103a 100644
--- a/src/ol/layer/Group.js
+++ b/src/ol/layer/Group.js
@@ -123,7 +123,7 @@ class LayerGroup extends BaseLayer {
     const layersArray = layers.getArray();
     for (let i = 0, ii = layersArray.length; i < ii; i++) {
       const layer = layersArray[i];
-      this.listenerKeys_[getUid(layer).toString()] = [
+      this.listenerKeys_[getUid(layer)] = [
         listen(layer, ObjectEventType.PROPERTYCHANGE, this.handleLayerChange_, this),
         listen(layer, EventType.CHANGE, this.handleLayerChange_, this)
       ];
@@ -138,8 +138,7 @@ class LayerGroup extends BaseLayer {
    */
   handleLayersAdd_(collectionEvent) {
     const layer = /** @type {import("./Base.js").default} */ (collectionEvent.element);
-    const key = getUid(layer).toString();
-    this.listenerKeys_[key] = [
+    this.listenerKeys_[getUid(layer)] = [
       listen(layer, ObjectEventType.PROPERTYCHANGE, this.handleLayerChange_, this),
       listen(layer, EventType.CHANGE, this.handleLayerChange_, this)
     ];
@@ -152,7 +151,7 @@ class LayerGroup extends BaseLayer {
    */
   handleLayersRemove_(collectionEvent) {
     const layer = /** @type {import("./Base.js").default} */ (collectionEvent.element);
-    const key = getUid(layer).toString();
+    const key = getUid(layer);
     this.listenerKeys_[key].forEach(unlistenByKey);
     delete this.listenerKeys_[key];
     this.changed();
diff --git a/src/ol/render/canvas/Replay.js b/src/ol/render/canvas/Replay.js
index 6ce0d83193..95aa1ceed3 100644
--- a/src/ol/render/canvas/Replay.js
+++ b/src/ol/render/canvas/Replay.js
@@ -597,9 +597,7 @@ class CanvasReplay extends VectorContext {
       switch (type) {
         case CanvasInstruction.BEGIN_GEOMETRY:
           feature = /** @type {import("../../Feature.js").default|import("../Feature.js").default} */ (instruction[1]);
-          if ((skipFeatures &&
-              skippedFeaturesHash[getUid(feature).toString()]) ||
-              !feature.getGeometry()) {
+          if ((skipFeatures && skippedFeaturesHash[getUid(feature)]) || !feature.getGeometry()) {
             i = /** @type {number} */ (instruction[2]);
           } else if (opt_hitExtent !== undefined && !intersects(
             opt_hitExtent, feature.getGeometry().getExtent())) {
diff --git a/src/ol/render/webgl/CircleReplay.js b/src/ol/render/webgl/CircleReplay.js
index 6184bcbd3a..65af1041dd 100644
--- a/src/ol/render/webgl/CircleReplay.js
+++ b/src/ol/render/webgl/CircleReplay.js
@@ -255,7 +255,7 @@ class WebGLCircleReplay extends WebGLReplay {
    * @inheritDoc
    */
   drawHitDetectionReplayOneByOne(gl, context, skippedFeaturesHash, featureCallback, opt_hitExtent) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex;
     featureIndex = this.startIndices.length - 2;
     end = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -269,9 +269,8 @@ class WebGLCircleReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         start = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid] === undefined &&
+        if (skippedFeaturesHash[getUid(feature)] === undefined &&
             feature.getGeometry() &&
             (opt_hitExtent === undefined || intersects(
               /** @type {Array<number>} */ (opt_hitExtent),
@@ -300,7 +299,7 @@ class WebGLCircleReplay extends WebGLReplay {
    * @param {Object} skippedFeaturesHash Ids of features to skip.
    */
   drawReplaySkipping_(gl, context, skippedFeaturesHash) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex, featureStart;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex, featureStart;
     featureIndex = this.startIndices.length - 2;
     end = start = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -314,9 +313,8 @@ class WebGLCircleReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         featureStart = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid]) {
+        if (skippedFeaturesHash[getUid(feature)]) {
           if (start !== end) {
             this.drawElements(gl, context, start, end);
           }
diff --git a/src/ol/render/webgl/LineStringReplay.js b/src/ol/render/webgl/LineStringReplay.js
index faf5a1954d..15aa0a34ac 100644
--- a/src/ol/render/webgl/LineStringReplay.js
+++ b/src/ol/render/webgl/LineStringReplay.js
@@ -536,7 +536,7 @@ class WebGLLineStringReplay extends WebGLReplay {
    * @param {Object} skippedFeaturesHash Ids of features to skip.
    */
   drawReplaySkipping_(gl, context, skippedFeaturesHash) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex, featureStart;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex, featureStart;
     featureIndex = this.startIndices.length - 2;
     end = start = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -548,9 +548,8 @@ class WebGLLineStringReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         featureStart = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid]) {
+        if (skippedFeaturesHash[getUid(feature)]) {
           if (start !== end) {
             this.drawElements(gl, context, start, end);
             gl.clear(gl.DEPTH_BUFFER_BIT);
@@ -572,7 +571,7 @@ class WebGLLineStringReplay extends WebGLReplay {
    * @inheritDoc
    */
   drawHitDetectionReplayOneByOne(gl, context, skippedFeaturesHash, featureCallback, opt_hitExtent) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex;
     featureIndex = this.startIndices.length - 2;
     end = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -584,9 +583,8 @@ class WebGLLineStringReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         start = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid] === undefined &&
+        if (skippedFeaturesHash[getUid(feature)] === undefined &&
             feature.getGeometry() &&
             (opt_hitExtent === undefined || intersects(
               /** @type {Array<number>} */ (opt_hitExtent),
diff --git a/src/ol/render/webgl/PolygonReplay.js b/src/ol/render/webgl/PolygonReplay.js
index 27d3ee7426..5418b66edd 100644
--- a/src/ol/render/webgl/PolygonReplay.js
+++ b/src/ol/render/webgl/PolygonReplay.js
@@ -927,7 +927,7 @@ class WebGLPolygonReplay extends WebGLReplay {
    * @inheritDoc
    */
   drawHitDetectionReplayOneByOne(gl, context, skippedFeaturesHash, featureCallback, opt_hitExtent) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex;
     featureIndex = this.startIndices.length - 2;
     end = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -939,9 +939,8 @@ class WebGLPolygonReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         start = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid] === undefined &&
+        if (skippedFeaturesHash[getUid(feature)] === undefined &&
             feature.getGeometry() &&
             (opt_hitExtent === undefined || intersects(
               /** @type {Array<number>} */ (opt_hitExtent),
@@ -970,7 +969,7 @@ class WebGLPolygonReplay extends WebGLReplay {
    * @param {Object} skippedFeaturesHash Ids of features to skip.
    */
   drawReplaySkipping_(gl, context, skippedFeaturesHash) {
-    let i, start, end, nextStyle, groupStart, feature, featureUid, featureIndex, featureStart;
+    let i, start, end, nextStyle, groupStart, feature, featureIndex, featureStart;
     featureIndex = this.startIndices.length - 2;
     end = start = this.startIndices[featureIndex + 1];
     for (i = this.styleIndices_.length - 1; i >= 0; --i) {
@@ -982,9 +981,8 @@ class WebGLPolygonReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         featureStart = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid]) {
+        if (skippedFeaturesHash[getUid(feature)]) {
           if (start !== end) {
             this.drawElements(gl, context, start, end);
             gl.clear(gl.DEPTH_BUFFER_BIT);
diff --git a/src/ol/render/webgl/TextureReplay.js b/src/ol/render/webgl/TextureReplay.js
index 2d7a068a87..102ada911d 100644
--- a/src/ol/render/webgl/TextureReplay.js
+++ b/src/ol/render/webgl/TextureReplay.js
@@ -244,7 +244,7 @@ class WebGLTextureReplay extends WebGLReplay {
     for (i = 0; i < ii; ++i) {
       image = images[i];
 
-      uid = getUid(image).toString();
+      uid = getUid(image);
       if (uid in texturePerImage) {
         texture = texturePerImage[uid];
       } else {
@@ -371,8 +371,7 @@ class WebGLTextureReplay extends WebGLReplay {
           this.startIndices[featureIndex] <= groupEnd) {
         const feature = this.startIndicesFeature[featureIndex];
 
-        const featureUid = getUid(feature).toString();
-        if (skippedFeaturesHash[featureUid] !== undefined) {
+        if (skippedFeaturesHash[getUid(feature)] !== undefined) {
           // feature should be skipped
           if (start !== end) {
             // draw the features so far
@@ -402,7 +401,7 @@ class WebGLTextureReplay extends WebGLReplay {
    * @inheritDoc
    */
   drawHitDetectionReplayOneByOne(gl, context, skippedFeaturesHash, featureCallback, opt_hitExtent) {
-    let i, groupStart, start, end, feature, featureUid;
+    let i, groupStart, start, end, feature;
     let featureIndex = this.startIndices.length - 1;
     const hitDetectionTextures = this.getHitDetectionTextures();
     for (i = hitDetectionTextures.length - 1; i >= 0; --i) {
@@ -415,9 +414,8 @@ class WebGLTextureReplay extends WebGLReplay {
           this.startIndices[featureIndex] >= groupStart) {
         start = this.startIndices[featureIndex];
         feature = this.startIndicesFeature[featureIndex];
-        featureUid = getUid(feature).toString();
 
-        if (skippedFeaturesHash[featureUid] === undefined &&
+        if (skippedFeaturesHash[getUid(feature)] === undefined &&
             feature.getGeometry() &&
             (opt_hitExtent === undefined || intersects(
               /** @type {Array<number>} */ (opt_hitExtent),
diff --git a/src/ol/renderer/Layer.js b/src/ol/renderer/Layer.js
index 4168482362..c1294826db 100644
--- a/src/ol/renderer/Layer.js
+++ b/src/ol/renderer/Layer.js
@@ -138,7 +138,7 @@ class LayerRenderer extends Observable {
        * @param {import("../PluggableMap.js").FrameState} frameState Frame state.
        */
       const postRenderFunction = function(tileSource, map, frameState) {
-        const tileSourceKey = getUid(tileSource).toString();
+        const tileSourceKey = getUid(tileSource);
         if (tileSourceKey in frameState.usedTiles) {
           tileSource.expireCache(frameState.viewState.projection,
             frameState.usedTiles[tileSourceKey]);
@@ -160,7 +160,7 @@ class LayerRenderer extends Observable {
    */
   updateUsedTiles(usedTiles, tileSource, z, tileRange) {
     // FIXME should we use tilesToDrawByZ instead?
-    const tileSourceKey = getUid(tileSource).toString();
+    const tileSourceKey = getUid(tileSource);
     const zKey = z.toString();
     if (tileSourceKey in usedTiles) {
       if (zKey in usedTiles[tileSourceKey]) {
@@ -206,7 +206,7 @@ class LayerRenderer extends Observable {
     opt_tileCallback,
     opt_this
   ) {
-    const tileSourceKey = getUid(tileSource).toString();
+    const tileSourceKey = getUid(tileSource);
     if (!(tileSourceKey in frameState.wantedTiles)) {
       frameState.wantedTiles[tileSourceKey] = {};
     }
diff --git a/src/ol/renderer/Map.js b/src/ol/renderer/Map.js
index 784d06a4a6..63be249396 100644
--- a/src/ol/renderer/Map.js
+++ b/src/ol/renderer/Map.js
@@ -123,9 +123,8 @@ class MapRenderer extends Disposable {
      * @return {?} Callback result.
      */
     function forEachFeatureAtCoordinate(feature, layer) {
-      const key = getUid(feature).toString();
       const managed = frameState.layerStates[getUid(layer)].managed;
-      if (!(key in frameState.skippedFeatureUids && !managed)) {
+      if (!(getUid(feature) in frameState.skippedFeatureUids && !managed)) {
         return callback.call(thisArg, feature, managed ? layer : null);
       }
     }
@@ -207,7 +206,7 @@ class MapRenderer extends Disposable {
    * @return {import("./Layer.js").default} Layer renderer.
    */
   getLayerRenderer(layer) {
-    const layerKey = getUid(layer).toString();
+    const layerKey = getUid(layer);
     if (layerKey in this.layerRenderers_) {
       return this.layerRenderers_[layerKey];
     } else {
diff --git a/src/ol/renderer/canvas/VectorLayer.js b/src/ol/renderer/canvas/VectorLayer.js
index 93d7d7be71..6af4ca10d4 100644
--- a/src/ol/renderer/canvas/VectorLayer.js
+++ b/src/ol/renderer/canvas/VectorLayer.js
@@ -244,7 +244,7 @@ class CanvasVectorLayerRenderer extends CanvasLayerRenderer {
          * @return {?} Callback result.
          */
         function(feature) {
-          const key = getUid(feature).toString();
+          const key = getUid(feature);
           if (!(key in features)) {
             features[key] = true;
             return callback.call(thisArg, feature, layer);
diff --git a/src/ol/renderer/canvas/VectorTileLayer.js b/src/ol/renderer/canvas/VectorTileLayer.js
index 04cadd75ab..174efbdabc 100644
--- a/src/ol/renderer/canvas/VectorTileLayer.js
+++ b/src/ol/renderer/canvas/VectorTileLayer.js
@@ -269,7 +269,7 @@ class CanvasVectorTileLayerRenderer extends CanvasTileLayerRenderer {
            * @return {?} Callback result.
            */
           function(feature) {
-            const key = getUid(feature).toString();
+            const key = getUid(feature);
             if (!(key in features)) {
               features[key] = true;
               return callback.call(thisArg, feature, layer);
diff --git a/src/ol/renderer/vector.js b/src/ol/renderer/vector.js
index 8d5a93ad4a..6ebb0f32ed 100644
--- a/src/ol/renderer/vector.js
+++ b/src/ol/renderer/vector.js
@@ -38,7 +38,7 @@ const GEOMETRY_RENDERERS = {
  * @return {number} Order.
  */
 export function defaultOrder(feature1, feature2) {
-  return getUid(feature1) - getUid(feature2);
+  return parseInt(getUid(feature1), 10) - parseInt(getUid(feature2), 10);
 }
 
 
diff --git a/src/ol/renderer/webgl/VectorLayer.js b/src/ol/renderer/webgl/VectorLayer.js
index df69728d13..2f8c96b5a8 100644
--- a/src/ol/renderer/webgl/VectorLayer.js
+++ b/src/ol/renderer/webgl/VectorLayer.js
@@ -128,7 +128,7 @@ class WebGLVectorLayerRenderer extends WebGLLayerRenderer {
          * @return {?} Callback result.
          */
         function(feature) {
-          const key = getUid(feature).toString();
+          const key = getUid(feature);
           if (!(key in features)) {
             features[key] = true;
             return callback.call(thisArg, feature, layer);
diff --git a/src/ol/source/Cluster.js b/src/ol/source/Cluster.js
index 74649500e4..ccbbbe5968 100644
--- a/src/ol/source/Cluster.js
+++ b/src/ol/source/Cluster.js
@@ -162,7 +162,7 @@ class Cluster extends VectorSource {
 
     for (let i = 0, ii = features.length; i < ii; i++) {
       const feature = features[i];
-      if (!(getUid(feature).toString() in clustered)) {
+      if (!(getUid(feature) in clustered)) {
         const geometry = this.geometryFunction(feature);
         if (geometry) {
           const coordinates = geometry.getCoordinates();
@@ -171,7 +171,7 @@ class Cluster extends VectorSource {
 
           let neighbors = this.source.getFeaturesInExtent(extent);
           neighbors = neighbors.filter(function(neighbor) {
-            const uid = getUid(neighbor).toString();
+            const uid = getUid(neighbor);
             if (!(uid in clustered)) {
               clustered[uid] = true;
               return true;
diff --git a/src/ol/source/Raster.js b/src/ol/source/Raster.js
index 7147f35870..a8534c2177 100644
--- a/src/ol/source/Raster.js
+++ b/src/ol/source/Raster.js
@@ -192,7 +192,7 @@ class RasterSource extends ImageSource {
     const layerStatesArray = getLayerStatesArray(this.renderers_);
 
     /**
-     * @type {Object<number, import("../layer/Layer.js").State>}
+     * @type {Object<string, import("../layer/Layer.js").State>}
      */
     const layerStates = {};
     for (let i = 0, ii = layerStatesArray.length; i < ii; ++i) {
diff --git a/src/ol/source/TileImage.js b/src/ol/source/TileImage.js
index c7228523a3..043fa21947 100644
--- a/src/ol/source/TileImage.js
+++ b/src/ol/source/TileImage.js
@@ -203,7 +203,7 @@ class TileImage extends UrlTile {
     if (this.tileGrid && (!thisProj || equivalent(thisProj, projection))) {
       return this.tileGrid;
     } else {
-      const projKey = getUid(projection).toString();
+      const projKey = getUid(projection);
       if (!(projKey in this.tileGridForProjection)) {
         this.tileGridForProjection[projKey] = getTileGridForProjection(projection);
       }
@@ -223,7 +223,7 @@ class TileImage extends UrlTile {
     const thisProj = this.getProjection(); if (!thisProj || equivalent(thisProj, projection)) {
       return this.tileCache;
     } else {
-      const projKey = getUid(projection).toString();
+      const projKey = getUid(projection);
       if (!(projKey in this.tileCacheForProjection)) {
         this.tileCacheForProjection[projKey] = new TileCache(this.tileCache.highWaterMark);
       }
@@ -379,7 +379,7 @@ class TileImage extends UrlTile {
     if (ENABLE_RASTER_REPROJECTION) {
       const proj = getProjection(projection);
       if (proj) {
-        const projKey = getUid(proj).toString();
+        const projKey = getUid(proj);
         if (!(projKey in this.tileGridForProjection)) {
           this.tileGridForProjection[projKey] = tilegrid;
         }
diff --git a/src/ol/source/UrlTile.js b/src/ol/source/UrlTile.js
index 0f26b3836e..74859e738a 100644
--- a/src/ol/source/UrlTile.js
+++ b/src/ol/source/UrlTile.js
@@ -84,7 +84,7 @@ class UrlTile extends TileSource {
 
     /**
      * @private
-     * @type {!Object<number, boolean>}
+     * @type {!Object<string, boolean>}
      */
     this.tileLoadingKeys_ = {};
 
diff --git a/src/ol/source/Vector.js b/src/ol/source/Vector.js
index 0ec3573092..9e5991f936 100644
--- a/src/ol/source/Vector.js
+++ b/src/ol/source/Vector.js
@@ -297,7 +297,7 @@ class VectorSource extends Source {
    * @protected
    */
   addFeatureInternal(feature) {
-    const featureKey = getUid(feature).toString();
+    const featureKey = getUid(feature);
 
     if (!this.addToIndex_(featureKey, feature)) {
       return;
@@ -383,7 +383,7 @@ class VectorSource extends Source {
 
     for (let i = 0, length = features.length; i < length; i++) {
       const feature = features[i];
-      const featureKey = getUid(feature).toString();
+      const featureKey = getUid(feature);
       if (this.addToIndex_(featureKey, feature)) {
         newFeatures.push(feature);
       }
@@ -391,7 +391,7 @@ class VectorSource extends Source {
 
     for (let i = 0, length = newFeatures.length; i < length; i++) {
       const feature = newFeatures[i];
-      const featureKey = getUid(feature).toString();
+      const featureKey = getUid(feature);
       this.setupChangeEvents_(featureKey, feature);
 
       const geometry = feature.getGeometry();
@@ -799,7 +799,7 @@ class VectorSource extends Source {
    */
   handleFeatureChange_(event) {
     const feature = /** @type {import("../Feature.js").default} */ (event.target);
-    const featureKey = getUid(feature).toString();
+    const featureKey = getUid(feature);
     const geometry = feature.getGeometry();
     if (!geometry) {
       if (!(featureKey in this.nullGeometryFeatures_)) {
@@ -855,8 +855,7 @@ class VectorSource extends Source {
     if (id !== undefined) {
       return id in this.idIndex_;
     } else {
-      const featureKey = getUid(feature).toString();
-      return featureKey in this.undefIdIndex_;
+      return getUid(feature) in this.undefIdIndex_;
     }
   }
 
@@ -924,7 +923,7 @@ class VectorSource extends Source {
    * @api
    */
   removeFeature(feature) {
-    const featureKey = getUid(feature).toString();
+    const featureKey = getUid(feature);
     if (featureKey in this.nullGeometryFeatures_) {
       delete this.nullGeometryFeatures_[featureKey];
     } else {
@@ -943,7 +942,7 @@ class VectorSource extends Source {
    * @protected
    */
   removeFeatureInternal(feature) {
-    const featureKey = getUid(feature).toString();
+    const featureKey = getUid(feature);
     this.featureChangeKeys_[featureKey].forEach(unlistenByKey);
     delete this.featureChangeKeys_[featureKey];
     const id = feature.getId();
diff --git a/src/ol/structs/RBush.js b/src/ol/structs/RBush.js
index 3a5dfc9fc8..3aaa847519 100644
--- a/src/ol/structs/RBush.js
+++ b/src/ol/structs/RBush.js
@@ -37,7 +37,7 @@ class RBush {
      * A mapping between the objects added to this rbush wrapper
      * and the objects that are actually added to the internal rbush.
      * @private
-     * @type {Object<number, Entry>}
+     * @type {Object<string, Entry>}
      */
     this.items_ = {};
 
diff --git a/src/ol/style/Fill.js b/src/ol/style/Fill.js
index 8381c35910..ad6e71bc7a 100644
--- a/src/ol/style/Fill.js
+++ b/src/ol/style/Fill.js
@@ -81,7 +81,7 @@ class Fill {
         if (Array.isArray(color) || typeof color == 'string') {
           this.checksum_ = 'f' + asString(/** @type {import("../Color.js").Color|string} */ (color));
         } else {
-          this.checksum_ = getUid(this.color_).toString();
+          this.checksum_ = getUid(this.color_);
         }
       } else {
         this.checksum_ = 'f-';
diff --git a/src/ol/style/Icon.js b/src/ol/style/Icon.js
index b5201313c2..7969cbf902 100644
--- a/src/ol/style/Icon.js
+++ b/src/ol/style/Icon.js
@@ -149,7 +149,7 @@ class Icon extends ImageStyle {
       5); // `imgSize` must be set when `image` is provided
 
     if ((src === undefined || src.length === 0) && image) {
-      src = /** @type {HTMLImageElement} */ (image).src || getUid(image).toString();
+      src = /** @type {HTMLImageElement} */ (image).src || getUid(image);
     }
     assert(src !== undefined && src.length > 0,
       6); // A defined and non-empty `src` or `image` must be provided
diff --git a/src/ol/style/Stroke.js b/src/ol/style/Stroke.js
index 4b058aae26..fc957545cb 100644
--- a/src/ol/style/Stroke.js
+++ b/src/ol/style/Stroke.js
@@ -259,7 +259,7 @@ class Stroke {
         if (typeof this.color_ === 'string') {
           this.checksum_ += this.color_;
         } else {
-          this.checksum_ += getUid(this.color_).toString();
+          this.checksum_ += getUid(this.color_);
         }
       } else {
         this.checksum_ += '-';
diff --git a/src/ol/util.js b/src/ol/util.js
index 2eee713b3d..2ba6870916 100644
--- a/src/ol/util.js
+++ b/src/ol/util.js
@@ -43,11 +43,11 @@ let uidCounter_ = 0;
  * as a strictly increasing sequence. Adapted from goog.getUid.
  *
  * @param {Object} obj The object to get the unique ID for.
- * @return {number} The unique ID for the object.
+ * @return {string} The unique ID for the object.
  * @api
  */
 export function getUid(obj) {
-  return obj.ol_uid || (obj.ol_uid = ++uidCounter_);
+  return obj.ol_uid || (obj.ol_uid = String(++uidCounter_));
 }
 
 /**
diff --git a/src/ol/webgl/Context.js b/src/ol/webgl/Context.js
index 7e2d0a45dc..a87932fffe 100644
--- a/src/ol/webgl/Context.js
+++ b/src/ol/webgl/Context.js
@@ -112,7 +112,7 @@ class WebGLContext extends Disposable {
   bindBuffer(target, buf) {
     const gl = this.getGL();
     const arr = buf.getArray();
-    const bufferKey = String(getUid(buf));
+    const bufferKey = getUid(buf);
     if (bufferKey in this.bufferCache_) {
       const bufferCacheEntry = this.bufferCache_[bufferKey];
       gl.bindBuffer(target, bufferCacheEntry.buffer);
@@ -139,7 +139,7 @@ class WebGLContext extends Disposable {
    */
   deleteBuffer(buf) {
     const gl = this.getGL();
-    const bufferKey = String(getUid(buf));
+    const bufferKey = getUid(buf);
     const bufferCacheEntry = this.bufferCache_[bufferKey];
     if (!gl.isContextLost()) {
       gl.deleteBuffer(bufferCacheEntry.buffer);
@@ -204,7 +204,7 @@ class WebGLContext extends Disposable {
    * @return {WebGLShader} Shader.
    */
   getShader(shaderObject) {
-    const shaderKey = String(getUid(shaderObject));
+    const shaderKey = getUid(shaderObject);
     if (shaderKey in this.shaderCache_) {
       return this.shaderCache_[shaderKey];
     } else {
diff --git a/test/spec/ol/render/webgl/circlereplay.test.js b/test/spec/ol/render/webgl/circlereplay.test.js
index 8f7d5d00e2..e807e8eb3a 100644
--- a/test/spec/ol/render/webgl/circlereplay.test.js
+++ b/test/spec/ol/render/webgl/circlereplay.test.js
@@ -229,7 +229,7 @@ describe('ol.render.webgl.CircleReplay', function() {
       replay.drawCircle(feature3.getGeometry(), feature3);
       replay.startIndices.push(replay.indices.length);
       const skippedFeatHash = {};
-      skippedFeatHash[getUid(feature2).toString()] = true;
+      skippedFeatHash[getUid(feature2)] = true;
 
       replay.drawReplay(gl, context, skippedFeatHash, false);
       expect(replay.setFillStyle_.calledOnce).to.be(true);
diff --git a/test/spec/ol/render/webgl/linestringreplay.test.js b/test/spec/ol/render/webgl/linestringreplay.test.js
index 842456e040..aa8b45ff21 100644
--- a/test/spec/ol/render/webgl/linestringreplay.test.js
+++ b/test/spec/ol/render/webgl/linestringreplay.test.js
@@ -336,7 +336,7 @@ describe('ol.render.webgl.LineStringReplay', function() {
       replay.drawLineString(feature3.getGeometry(), feature3);
       replay.startIndices.push(replay.indices.length);
       const skippedFeatHash = {};
-      skippedFeatHash[getUid(feature2).toString()] = true;
+      skippedFeatHash[getUid(feature2)] = true;
 
       replay.drawReplay(gl, context, skippedFeatHash, false);
       expect(replay.setStrokeStyle_.calledOnce).to.be(true);
diff --git a/test/spec/ol/render/webgl/polygonreplay.test.js b/test/spec/ol/render/webgl/polygonreplay.test.js
index 8663e76231..4283675128 100644
--- a/test/spec/ol/render/webgl/polygonreplay.test.js
+++ b/test/spec/ol/render/webgl/polygonreplay.test.js
@@ -457,7 +457,7 @@ describe('ol.render.webgl.PolygonReplay', function() {
       replay.drawPolygon(feature3.getGeometry(), feature3);
       replay.startIndices.push(replay.indices.length);
       const skippedFeatHash = {};
-      skippedFeatHash[getUid(feature2).toString()] = true;
+      skippedFeatHash[getUid(feature2)] = true;
 
       replay.drawReplay(gl, context, skippedFeatHash, false);
       expect(replay.setFillStyle_.calledOnce).to.be(true);