fix(overlays): fire show/hide event on shown changed

packages/overlays/src/LocalOverlayController.js

@@ -7,6 +7,8 @@ async function __preloadPopper() {
 }
 export class LocalOverlayController {
   constructor(params = {}) {
+    this.__fakeExtendsEventTarget();
+
     // TODO: Instead of in constructor, prefetch it or use a preloader-manager to load it during idle time
     this.constructor.popperModule = __preloadPopper();
     this.__mergePopperConfigs(params.popperConfig || {});
@@ -165,11 +167,19 @@ export class LocalOverlayController {
       if (this.trapsKeyboardFocus) this._setupTrapsKeyboardFocus();
       if (this.hidesOnOutsideClick) this._setupHidesOnOutsideClick();
       if (this.hidesOnEsc) this._setupHidesOnEsc();
+
+      if (this._prevShown === false) {
+        this.dispatchEvent(new Event('show'));
+      }
     } else {
       this._updateContent();
       this.invokerNode.setAttribute('aria-expanded', false);
       if (this.hidesOnOutsideClick) this._teardownHidesOnOutsideClick();
       if (this.hidesOnEsc) this._teardownHidesOnEsc();
+
+      if (this._prevShown === true) {
+        this.dispatchEvent(new Event('hide'));
+      }
     }
     this._prevShown = shown;
     this._prevData = data;
@@ -301,4 +311,13 @@ export class LocalOverlayController {
       ...this.popperConfig,
     });
   }
+
+  // TODO: this method has to be removed when EventTarget polyfill is available on IE11
+  // issue: https://gitlab.ing.net/TheGuideComponents/lion-element/issues/12
+  __fakeExtendsEventTarget() {
+    const delegate = document.createDocumentFragment();
+    ['addEventListener', 'dispatchEvent', 'removeEventListener'].forEach(funcName => {
+      this[funcName] = (...args) => delegate[funcName](...args);
+    });
+  }
 }

packages/overlays/test/LocalOverlayController.test.js

@@ -1,4 +1,5 @@
 import { expect, fixture, html, aTimeout, defineCE, unsafeStatic } from '@open-wc/testing';
+import sinon from 'sinon';
 import Popper from 'popper.js/dist/popper.min.js';
 
 import { keyUpOn } from '@polymer/iron-test-helpers/mock-interactions.js';
@@ -898,4 +899,27 @@ describe('LocalOverlayController', () => {
       expect(ctrl.isShown).to.equal(true);
     });
   });
+
+  describe('events', () => {
+    it('fires "show" event once overlay becomes shown', async () => {
+      const showSpy = sinon.spy();
+      const ctrl = new LocalOverlayController();
+      ctrl.addEventListener('show', showSpy);
+      await ctrl.show();
+      expect(showSpy.callCount).to.equal(1);
+      await ctrl.show();
+      expect(showSpy.callCount).to.equal(1);
+    });
+
+    it('fires "hide" event once overlay becomes hidden', async () => {
+      const hideSpy = sinon.spy();
+      const ctrl = new LocalOverlayController();
+      ctrl.addEventListener('hide', hideSpy);
+      ctrl.hide();
+      expect(hideSpy.callCount).to.equal(0);
+      await ctrl.show();
+      ctrl.hide();
+      expect(hideSpy.callCount).to.equal(1);
+    });
+  });
 });