Write the correct SRS code in EsriJSON

src/ol/format/EsriJSON.js

@@ -207,16 +207,14 @@ class EsriJSON extends JSONFeature {
     const geometry = feature.getGeometry();
     if (geometry) {
       object['geometry'] = writeGeometry(geometry, opt_options);
-      if (opt_options && opt_options.featureProjection) {
+      const projection =
+        opt_options &&
+        (opt_options.dataProjection || opt_options.featureProjection);
+      if (projection) {
         object['geometry'][
           'spatialReference'
         ] = /** @type {EsriJSONSpatialReferenceWkid} */ ({
-          wkid: Number(
+          wkid: Number(getProjection(projection).getCode().split(':').pop()),
-            getProjection(opt_options.featureProjection)
-              .getCode()
-              .split(':')
-              .pop()
-          ),
         });
       }
       delete properties[feature.getGeometryName()];

test/spec/ol/format/esrijson.test.js

@@ -1763,15 +1763,38 @@ describe('ol.format.EsriJSON', function () {
       expect(esrijson.attributes).to.eql({});
     });
 
-    it('adds the projection inside the geometry correctly', function () {
+    it('adds the projection inside the geometry correctly when featureProjection is set', function () {
       const str = JSON.stringify(data);
       const array = format.readFeatures(str);
       const esrijson = format.writeFeaturesObject(array, {
-        featureProjection: 'EPSG:4326',
+        featureProjection: 'EPSG:3857',
       });
-      esrijson.features.forEach(function (feature) {
+      esrijson.features.forEach(function (feature, i) {
+        const spatialReference = feature.geometry.spatialReference;
+        expect(Number(spatialReference.wkid)).to.equal(3857);
+        expect(feature.geometry.paths[0]).to.eql(
+          array[i].getGeometry().getCoordinates()
+        );
+      });
+    });
+
+    it('adds the projection inside the geometry correctly when dataProjection is set', function () {
+      const str = JSON.stringify(data);
+      const array = format.readFeatures(str);
+      const esrijson = format.writeFeaturesObject(array, {
+        dataProjection: 'EPSG:4326',
+        featureProjection: 'EPSG:3857',
+      });
+      esrijson.features.forEach(function (feature, i) {
         const spatialReference = feature.geometry.spatialReference;
         expect(Number(spatialReference.wkid)).to.equal(4326);
+        expect(feature.geometry.paths[0]).to.eql(
+          array[i]
+            .getGeometry()
+            .clone()
+            .transform('EPSG:3857', 'EPSG:4326')
+            .getCoordinates()
+        );
       });
     });
   });