feat: Button Toggle: Add ability for consumers to handle toggling pressed state

components/button/button-toggle.js

@@ -2,6 +2,7 @@ import { css, html, LitElement } from 'lit';
 
 /**
  * A button container component for button toggles.
+ * @fires d2l-button-toggle-before-change - Dispatched before pressed state is updated. Can be canceled to allow the consumer to handle toggling pressed state. This is useful if something needs to happen prior to the pressed state being toggled.
  */
 class ButtonToggle extends LitElement {
 
@@ -79,9 +80,16 @@ class ButtonToggle extends LitElement {
 	}
 
 	async _handleClick(pressed) {
-		this.pressed = pressed;
-		await this.updateComplete;
-		this.focus();
+		const beforeToggleEvent = new CustomEvent('d2l-button-toggle-before-change', {
+			detail: {
+				update: (newPressed) => this._updatePressedState(newPressed)
+			},
+			cancelable: true
+		});
+		this.dispatchEvent(beforeToggleEvent);
+		if (beforeToggleEvent.defaultPrevented) return;
+
+		this._updatePressedState(pressed);
 	}
 
 	_handleNotPressedClick() {
@@ -92,6 +100,12 @@ class ButtonToggle extends LitElement {
 		this._handleClick(false);
 	}
 
+	async _updatePressedState(newPressed) {
+		this.pressed = newPressed;
+		await this.updateComplete;
+		this.focus();
+	}
+
 }
 
 customElements.define('d2l-button-toggle', ButtonToggle);

components/button/demo/button-toggle.html

@@ -54,6 +54,26 @@ <h2>Toggle Button (disabled)</h2>
 				</template>
 			</d2l-demo-snippet>
 
+			<h2>Toggle Button (with consumer specifying when to toggle)</h2>
+
+			<d2l-demo-snippet>
+				<template>
+					<d2l-button-toggle id="toggle-button-icon-promise-delay">
+						<d2l-button-icon slot="not-pressed" icon="tier1:pin-hollow" text="Unpinned, click to pin."></d2l-button-icon>
+						<d2l-button-icon slot="pressed" icon="tier1:pin-filled" text="Pinned, click to unpin."></d2l-button-icon>
+					</d2l-button-toggle>
+					<script>
+						document.querySelector('#toggle-button-icon-promise-delay').addEventListener('d2l-button-toggle-before-change', e => {
+							e.preventDefault();
+							setTimeout(() => {
+								e.detail.update(!e.target.pressed);
+							}, 2000);
+						});
+						document.querySelector('#toggle-button-icon-promise-delay').addEventListener('d2l-button-toggle-change', e => console.log(e));
+					</script>
+				</template>
+			</d2l-demo-snippet>
+
 		</d2l-demo-page>
 
 	</body>

components/button/test/button-toggle.test.js

@@ -63,4 +63,35 @@ describe('d2l-button-toggle', () => {
 
 	});
 
+	describe('consumer manages state', () => {
+
+		let el;
+		beforeEach(async() => {
+			el = await fixture(html`
+				<d2l-button-toggle>
+					<d2l-button-icon slot="not-pressed" icon="tier1:pin-hollow" text="Unpinned, click to pin."></d2l-button-icon>
+					<d2l-button-icon slot="pressed" icon="tier1:pin-filled" text="Pinned, click to unpin."></d2l-button-icon>
+				</d2l-button-toggle>
+			`);
+		});
+
+		it('click with no state management', async() => {
+			el.addEventListener('d2l-button-toggle-before-change', (e) => {
+				e.preventDefault();
+			});
+			await clickElem(el.querySelector('[slot="not-pressed"]'));
+			expect(el.pressed).to.equal(false);
+		});
+
+		it('click once with state management', async() => {
+			el.addEventListener('d2l-button-toggle-before-change', (e) => {
+				e.preventDefault();
+				e.detail.update(!e.target.pressed);
+			});
+			clickElem(el.querySelector('[slot="not-pressed"]'));
+			const e = await oneEvent(el, 'd2l-button-toggle-change');
+			expect(e.target.pressed).to.equal(true);
+		});
+	});
+
 });