Web Components (custom elements + shadow DOM) क्या हैं?

Web Components (custom elements + shadow DOM) क्या हैं? – HTML · IT इंटरव्यू अभ्यास

class UserCard extends HTMLElement {
  connectedCallback() {            // lifecycle: runs when added to the page
    const shadow = this.attachShadow({ mode: "open" }); // create shadow DOM
    shadow.innerHTML = `
      <style> h2 { color: blue; } </style>
      <h2>${this.getAttribute("name")}</h2>
      <slot></slot>
    `;
  }
}
customElements.define("user-card", UserCard); // name MUST contain a hyphen

connectedCallback()    // added to DOM
disconnectedCallback() // removed from DOM (cleanup)
attributeChangedCallback(name, old, val) // an observed attribute changed
static get observedAttributes() { return ["name"]; }

एक custom element परिभाषित करना

Shadow DOM = वास्तविक encapsulation

Lifecycle callbacks

यह क्यों महत्वपूर्ण है