Use proj4 from the proj4 package instead of the global

examples/wms-image-custom-proj.js

@@ -7,23 +7,26 @@ import {fromLonLat} from '../src/ol/proj.js';
 import _ol_proj_Projection_ from '../src/ol/proj/Projection.js';
 import _ol_source_ImageWMS_ from '../src/ol/source/ImageWMS.js';
 import {register} from '../src/ol/proj/proj4.js';
+import proj4 from 'proj4';
 
 
 // Transparent Proj4js support:
 //
-// EPSG:21781 is known to Proj4js because its definition was loaded in the html.
-// Now when we create an ol.proj.Projection instance with the 'EPSG:21781' code,
-// OpenLayers will pick up parameters like units and transform functions from
-// Proj4js.
+// EPSG:21781 is known to Proj4js because its definition is registered by
+// calling proj4.defs(). Now when we create an ol/proj/Projection instance with
+// the 'EPSG:21781' code, OpenLayers will pick up the transform functions from
+// Proj4js. To get the registered ol/proj/Projection instance with other
+// parameters like units and axis orientation applied from Proj4js, use
+// `ol/proj#get('EPSG:21781')`.
 //
 // Note that we are setting the projection's extent here, which is used to
 // determine the view resolution for zoom level 0. Recommended values for a
 // projection's validity extent can be found at https://epsg.io/.
-//
-// If you use Proj4js only to transform coordinates, you don't even need to
-// create an ol.proj.Projection instance. ol.proj.get() will take care of it
-// internally.
 
+proj4.defs('EPSG:21781',
+    '+proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 ' +
+    '+x_0=600000 +y_0=200000 +ellps=bessel ' +
+    '+towgs84=660.077,13.551,369.344,2.484,1.783,2.939,5.66 +units=m +no_defs');
 register(proj4);
 
 var projection = new _ol_proj_Projection_({