Created
July 29, 2025 10:11
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Demo of foundational tags like img, b, button implemented using Web Components
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="UTF-8"> | |
| <title>Custom Elements Demo</title> | |
| </head> | |
| <body> | |
| <custom-b>Hello, bold world!</custom-b> | |
| <br><br> | |
| <custom-img src="https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/PNG_transparency_demonstration_1.png/320px-PNG_transparency_demonstration_1.png"></custom-img> | |
| <br><br> | |
| <custom-button id="mybtn">Click me</custom-button> | |
| <script> | |
| // <custom-b> | |
| customElements.define('custom-b', class extends HTMLElement { | |
| connectedCallback() { | |
| this.style.fontWeight = 'bold'; | |
| } | |
| }); | |
| // <custom-img> | |
| customElements.define('custom-img', class extends HTMLElement { | |
| constructor() { | |
| super(); | |
| this.attachShadow({ mode: 'open' }); | |
| this.canvas = document.createElement('canvas'); | |
| this.ctx = this.canvas.getContext('2d'); | |
| this.shadowRoot.appendChild(this.canvas); | |
| } | |
| static get observedAttributes() { | |
| return ['src']; | |
| } | |
| attributeChangedCallback(name, _, value) { | |
| if (name === 'src') this.loadImage(value); | |
| } | |
| async loadImage(src) { | |
| const img = new Image(); | |
| img.crossOrigin = 'anonymous'; | |
| img.onload = () => { | |
| this.canvas.width = img.naturalWidth; | |
| this.canvas.height = img.naturalHeight; | |
| this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height); | |
| this.ctx.drawImage(img, 0, 0); | |
| }; | |
| img.onerror = () => { | |
| this.canvas.width = this.canvas.height = 0; | |
| }; | |
| img.src = src; | |
| } | |
| connectedCallback() { | |
| const style = document.createElement('style'); | |
| style.textContent = ` | |
| canvas { | |
| display: block; | |
| max-width: 100%; | |
| height: auto; | |
| } | |
| `; | |
| this.shadowRoot.prepend(style); | |
| if (this.hasAttribute('src')) { | |
| this.loadImage(this.getAttribute('src')); | |
| } | |
| } | |
| }); | |
| // <custom-button> | |
| customElements.define('custom-button', class extends HTMLElement { | |
| constructor() { | |
| super(); | |
| this.attachShadow({ mode: 'open' }); | |
| const div = document.createElement('div'); | |
| div.setAttribute('tabindex', '0'); | |
| div.setAttribute('role', 'button'); | |
| div.innerHTML = `<slot></slot>`; | |
| const style = document.createElement('style'); | |
| style.textContent = ` | |
| div { | |
| all: unset; | |
| display: inline-block; | |
| padding: 0.4em 1em; | |
| border: 1px solid #ccc; | |
| border-radius: 4px; | |
| background: #eee; | |
| cursor: pointer; | |
| font: inherit; | |
| } | |
| div:focus { | |
| outline: 2px solid blue; | |
| } | |
| div:active { | |
| background: #ddd; | |
| } | |
| `; | |
| this.shadowRoot.append(style, div); | |
| this.btn = div; | |
| } | |
| connectedCallback() { | |
| this.btn.addEventListener('keydown', e => { | |
| if (e.key === 'Enter' || e.key === ' ') { | |
| this.btn.click(); | |
| e.preventDefault(); | |
| } | |
| }); | |
| this.btn.addEventListener('click', e => { | |
| this.dispatchEvent(new MouseEvent('click', { bubbles: true, composed: true })); | |
| }); | |
| } | |
| }); | |
| // Example click listener | |
| document.getElementById('mybtn').addEventListener('click', () => { | |
| alert('Button clicked!'); | |
| }); | |
| </script> | |
| </body> | |
| </html> |
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