BrightspaceUI · AllanKerr · May 19, 2020 · May 11, 2020 · May 11, 2020 · May 12, 2020
diff --git a/components/expand-collapse/demo/expand-collapse.html b/components/expand-collapse/demo/expand-collapse.html
@@ -0,0 +1,57 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<meta http-equiv="X-UA-Compatible" content="ie=edge">
+	<meta charset="UTF-8">
+	<link rel="stylesheet" href="../../demo/styles.css" type="text/css">
+	<script src="/node_modules/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script>
+	<script type="module">
+		import '../../button/button.js';
+		import '../../demo/demo-page.js';
+		import '../expand-collapse.js';
+	</script>
+</head>
+
+<body unresolved>
+
+	<d2l-demo-page page-title="d2l-expand-collapse">
+
+		<h2>Default</h2>
+		<d2l-demo-snippet>
+			<template>
+				<d2l-button primary>Toggle</d2l-button>
+				<d2l-expand-collapse>
+					<p>
+					Yar Pirate Ipsum
+					Crow's nest chase guns coxswain belay coffer jib Shiver me timbers tackle piracy Buccaneer. Overhaul topsail Cat o'nine
+					tails lee wherry Sink me smartly ballast Sail ho hardtack. Bowsprit aft quarterdeck killick pirate black jack hands
+					crimp interloper yawl.
+					</p>
+					<ul>
+						<li>Coffee</li>
+						<li>Tea</li>
+						<li>Milk</li>
+					</ul>
+					<p>
+					Me trysail gangplank Plate Fleet Sink me hang the jib lanyard parrel square-rigged stern. Gangplank chandler brigantine
+					spyglass scurvy rope's end plunder lugger topmast trysail. Admiral of the Black cackle fruit hearties maroon bounty
+					Blimey yo-ho-ho sutler pillage boom.
+					</p>
+				</d2l-expand-collapse>
+				<script type="module">
+					const button = document.querySelector('d2l-button');
+					button.addEventListener('click', () => {
+						const section = document.querySelector('d2l-expand-collapse');
+						section.expanded = !section.expanded;
+					});
+				</script>
+			</template>
+		</d2l-demo-snippet>
+
+	</d2l-demo-page>
+
+</body>
+
+</html>
diff --git a/components/expand-collapse/expand-collapse.js b/components/expand-collapse/expand-collapse.js
@@ -0,0 +1,140 @@
+import { css, html, LitElement } from 'lit-element/lit-element.js';
+import ResizeObserver from 'resize-observer-polyfill/dist/ResizeObserver.es.js';
+import { styleMap } from 'lit-html/directives/style-map.js';
+
+const reduceMotion = matchMedia('(prefers-reduced-motion: reduce)').matches;
+
+const states = {
+	COLLAPSING: 'collapsing', // in the process of collapsing
+	COLLAPSED: 'collapsed', // fully collapsed
+	EXPANDING: 'expanding', // in the process of expanding
+	EXPANDED: 'expanded', // fully expanded
+};
+
+class ExpandCollapse extends LitElement {
+
+	static get properties() {
+		return {
+			expanded: { type: Boolean, reflect: true },
+			_height: { type: Number },
+			_state: { type: String }
+		};
+	}
+
+	static get styles() {
+		return css`
+			:host {
+				display: block;
+			}
+
+			:host([hidden]) {
+				display: none;
+			}
+
+			.d2l-expand-collapse-container {
+				display: none;
+				height: 0px;
+				overflow: hidden;
+				transition: height 400ms cubic-bezier(0, 0.7, 0.5, 1);
+			}
+
+			.d2l-expand-collapse-container:not([data-state="collapsed"]) {
+				display: block;
+			}
+
+			.d2l-expand-collapse-container[data-state="expanded"] {
+				overflow: visible;
+			}
+
+			/* prevent margin colapse on slotted children */
+			.d2l-expand-collapse-content:before,
+			.d2l-expand-collapse-content:after {
+				content: ' ';
+				display: table;
+			}
+
+			@media (prefers-reduced-motion: reduce) {
+				.d2l-expand-collapse-container {
+					transition: none;
+				}
+			}
+		`;
+	}
+
+	constructor() {
+		super();
+		this._onContentResize = this._onContentResize.bind(this);
+		this.expanded = false;
+		this._state = states.COLLAPSED;
+	}
+
+	get expanded() {
+		return this._expanded;
+	}
+
+	set expanded(val) {
+		const oldVal = this._expanded;
+		if (oldVal !== val) {
+			this._expanded = val;
+			this.requestUpdate('expanded', oldVal);
+			this._expandedChanged(val);
+		}
+	}
+
+	firstUpdated() {
+		super.firstUpdated();
+
+		const content = this.shadowRoot.querySelector('.d2l-expand-collapse-content');
+		this._resizeObserver = new ResizeObserver(this._onContentResize);
+		this._resizeObserver.observe(content);
+	}
+
+	render() {
+		const styles = {
+			height: this.expanded ? `${this._height}px` : null
+		};
+		return html`
+			<div class="d2l-expand-collapse-container" data-state=${this._state} @transitionend=${this._onTransitionEnd} style=${styleMap(styles)}>
+				<div class="d2l-expand-collapse-content">
+					<slot></slot>
+				</div>
+			</div>
+		`;
+	}
+
+	_expandedChanged(val) {
+		if (val) {
+			this._state = reduceMotion ? states.EXPANDED : states.EXPANDING;
+			this._updateHeight();
+		} else {
+			this._state = reduceMotion ? states.COLLAPSED : states.COLLAPSING;
+			this._height = null;
+		}
+	}
+
+	_getContent() {
+		return this.shadowRoot.querySelector('.d2l-expand-collapse-content');
+	}
+
+	_onTransitionEnd() {
+		if (this._state === states.EXPANDING) {
+			this._state = states.EXPANDED;
+		} else if (this._state === states.COLLAPSING) {
+			this._state = states.COLLAPSED;
+		}
+	}
+
+	_onContentResize() {
+		if (!this.expanded) {
+			return;
+		}
+		this._updateHeight();
+	}
+
+	_updateHeight() {
+		const content = this._getContent();
+		this._height = content.scrollHeight;
+	}
+
+}
+customElements.define('d2l-expand-collapse', ExpandCollapse);
diff --git a/index.html b/index.html
@@ -57,6 +57,7 @@ <h2 class="d2l-heading-3">Components</h2>
 				<li><a href="components/dropdown/demo/dropdown-tabs.html">d2l-dropdown-tabs</a></li>
 			</ul>
 		</li>
+		<li><a href="components/expand-collapse/demo/expand-collapse.html">d2l-expand-collapse</a></li>
 		<li><a href="components/focus-trap/demo/focus-trap.html">d2l-focus-trap</a></li>
 		<li><a href="components/hierarchical-view/demo/hierarchical-view.html">d2l-hierarchical-view</a></li>
 		<li><a href="components/icons/demo/icon.html">d2l-icon</a></li>