Web Components
Master Web Components — Custom Elements, Shadow DOM, HTML Templates, and building reusable, framework-agnostic UI components.
55 min•By Priygop Team•Last updated: Feb 2026
Web Components Fundamentals
- Custom Elements: Define new HTML tags — customElements.define('my-card', MyCard). Lifecycle callbacks: connectedCallback, disconnectedCallback, attributeChangedCallback
- Shadow DOM: Encapsulated DOM subtree — styles and markup are isolated. this.attachShadow({mode: 'open'}). External CSS can't affect shadow DOM and vice versa
- HTML Templates: <template> element — parsed but not rendered until cloned. Efficient reusable markup. <slot> for content projection (like React children)
- Slots: Named slots for flexible content — <slot name='header'> accepts <div slot='header'>. Default slot catches unslotted content. Compose complex components
- Attributes & Properties: Observed attributes trigger attributeChangedCallback — static get observedAttributes() { return ['color', 'size']; }. Reflect as properties for JS API
- Framework Compatibility: Web Components work in React, Vue, Angular, Svelte — truly framework-agnostic. Use for design system primitives that must work everywhere