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Web Component for a toggle section: an expandable collapsible block with a heading.
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class ToggleSection extends HTMLElement { | |
constructor() { | |
super(); | |
} | |
connectedCallback() { | |
this.render(); | |
this.btn.addEventListener('click', () => { | |
this.setAttribute('open', this.getAttribute('open') === 'true' ? 'false' : 'true'); | |
}) | |
} | |
attributeChangedCallback(name) { | |
if (name === 'open') { | |
this.switchState() | |
} | |
} | |
render() { | |
const tmpl = document.createElement('template'); | |
tmpl.innerHTML = getTemplateHTML(); | |
this.setAttribute('role', 'region'); | |
this.attachShadow({ mode: 'open' }); | |
this.shadowRoot.appendChild(tmpl.content.cloneNode(true)); | |
this.btn = this.shadowRoot.querySelector('h3 button'); | |
const oldHeading = this.querySelector(':first-child'); | |
let level = parseInt(oldHeading.tagName.substr(1)); | |
this.heading = this.shadowRoot.querySelector('h3') | |
if (!level) { | |
console.warn('The first element inside each <toggle-section> should be a heading of an appropriate level.') | |
} | |
if (level && level !== 3) { | |
this.heading.setAttribute('aria-level', level) | |
} | |
this.btn.innerHTML = `${this.btn.innerHTML} <span>${oldHeading.textContent}</span>`; | |
oldHeading.parentNode.removeChild(oldHeading); | |
} | |
// The main state switching function | |
switchState() { | |
let expanded = this.getAttribute('open') === 'true' || false; | |
this.btn.setAttribute('aria-expanded', expanded); | |
this.shadowRoot.querySelector('.content').hidden = !expanded; | |
} | |
static get observedAttributes() { | |
return ['open'] | |
} | |
}; | |
const getTemplateHTML = () => { | |
const templateHTML = ` | |
<h3> | |
<button aria-expanded="false"> | |
<svg aria-hidden="true" focusable="false" viewBox="0 0 10 10"> | |
<rect class="vert" height="8" width="2" y="1" x="4"/> | |
<rect height="2" width="8" y="4" x="1"/> | |
</svg> | |
</button> | |
</h3> | |
<div class="content" hidden> | |
<slot></slot> | |
</div> | |
<style> | |
h3 { | |
margin: 0; | |
font-family: var(--heading-font-family); | |
font-size: var(--heading-font-size); | |
} | |
h3 button { | |
all: inherit; | |
box-sizing: border-box; | |
display: flex; | |
align-items: center; | |
width: 100%; | |
padding: 1em 0; | |
cursor: pointer; | |
} | |
h3 button span { | |
border-bottom: 2px solid transparent; | |
margin-bottom: -2px; | |
} | |
h3 button:focus span { | |
border-color: var(--primary-color); | |
} | |
button svg { | |
height: 1rem; | |
margin-right: 0.5em; | |
flex-shrink: 0; | |
} | |
[aria-expanded="true"] .vert { | |
display: none; | |
} | |
[aria-expanded] rect { | |
fill: currentColor; | |
} | |
div.content { | |
padding-bottom: 1em; | |
} | |
</style>` | |
return templateHTML; | |
}; | |
const ToggleSectionComponent = () => { | |
if (!'content' in document.createElement('template') || !document.head.attachShadow) { | |
return; | |
} | |
window.customElements.define('toggle-section', ToggleSection); | |
}; | |
export default ToggleSectionComponent; |
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