Unknown Elements vs Undefined Custom Elements

📘 手冊

• Google ⟩ Unknown elements vs. undefined custom elements

💾 程式

• replit

注意：

• 沒有 "-" 的標籤 (如：<nosuchtag>) 會被視為 HTMLUnknownElement，

• 但有 "-" 的標籤 (如：<undefined-element>) 會被視為 HTMLElement❗️

const {log} = console;

[
    // <tabs> is an "unknown" element
    tag('tabs') instanceof HTMLUnknownElement,      // true

    // <x-tabs> is an "undefined" custom element
    tag('x-tabs') instanceof HTMLElement,           // true

].forEach(x => log(x));

// helper function
function tag(name){
    return document.createElement(name);
}