Created
May 9, 2024 10:36
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a MutationObserver that defines custom elements when they appear in the DOM
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| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <meta charset="UTF-8"> | |
| <meta name="viewport" content="width=device-width" /> | |
| <title>‎</title> | |
| <link rel="icon" href="data:image/x-icon;base64,AA"> | |
| </head> | |
| <body> | |
| <button id="add-item">Add item</button> | |
| <div id="items"></div> | |
| <script> | |
| document.getElementById("add-item").onclick = () => | |
| document.getElementById("items").appendChild(document.createElement("my-item")) | |
| </script> | |
| <template id="my-item"> | |
| <div>item</div> | |
| </template> | |
| <script> | |
| class MyItem extends HTMLElement { | |
| static tagName = "my-item" | |
| constructor() { | |
| super() | |
| this.attachShadow({ mode: "open" }).appendChild( | |
| document.querySelector("template#my-item").content.cloneNode(true) | |
| ) | |
| } | |
| } | |
| const myWebComponents = new Map() | |
| myWebComponents.set(MyItem.tagName, MyItem) | |
| const observer = new MutationObserver((mutationList) => { | |
| for (const mutation of mutationList) if (mutation.type === "childList") | |
| mutation.addedNodes.forEach(addedNode => { | |
| const tagName = addedNode.tagName?.toLowerCase() | |
| if (customElements.get(tagName)) return | |
| const Component = myWebComponents.get(tagName) | |
| if (Component) { | |
| console.info("Define custom element", tagName) | |
| customElements.define(tagName, Component) | |
| } | |
| }) | |
| }) | |
| observer.observe(document.body, { attributes: false, childList: true, subtree: true }); | |
| </script> | |
| </body> | |
| </html> |
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