Re-order the arguments list to onSetup

app/assets/javascripts/editor/extensions/example_source_editor_extension.js

@@ -16,11 +16,11 @@ export class MyFancyExtension {
    * actions, keystrokes, update options, etc.
    * Is called only once before the extension gets registered
    *
-   * @param { Object } [setupOptions]  The setupOptions object
    * @param { Object } [instance] The Source Editor instance
+   * @param { Object } [setupOptions]  The setupOptions object
    */
   // eslint-disable-next-line class-methods-use-this,no-unused-vars
-  onSetup(setupOptions, instance) {}
+  onSetup(instance, setupOptions) {}
 
   /**
    * The first thing called after the extension is

app/assets/javascripts/editor/source_editor_instance.js

@@ -153,7 +153,7 @@ export default class EditorInstance {
     const extensionInstance = new EditorExtension(extension);
     const { setupOptions, obj: extensionObj } = extensionInstance;
     if (extensionObj.onSetup) {
-      extensionObj.onSetup(setupOptions, this);
+      extensionObj.onSetup(this, setupOptions);
     }
     if (extensionsStore) {
       this.registerExtension(extensionInstance, extensionsStore);

spec/frontend/editor/helpers.js

@@ -31,7 +31,7 @@ export const SEConstExt = () => {
 
 export function SEWithSetupExt() {
   return {
-    onSetup: (setupOptions = {}, instance) => {
+    onSetup: (instance, setupOptions = {}) => {
       if (setupOptions && !Array.isArray(setupOptions)) {
         Object.entries(setupOptions).forEach(([key, value]) => {
           Object.assign(instance, {

spec/frontend/editor/source_editor_instance_spec.js

@@ -424,7 +424,7 @@ describe('Source Editor Instance', () => {
           definition: MyFullExtWithCallbacks,
           setupOptions: defSetupOptions,
         });
-        expect(onSetup).toHaveBeenCalledWith(defSetupOptions, seInstance);
+        expect(onSetup).toHaveBeenCalledWith(seInstance, defSetupOptions);
         expect(onUse).toHaveBeenCalledWith(seInstance);
       });