---

name: javascript-author description: Write vanilla JavaScript for Web Components with functional core, imperative shell. Use when creating JavaScript files, building interactive components, or writing any client-side code. allowed-tools: Read, Write, Edit, Glob, Grep

JavaScript Authoring Skill

Write modern vanilla JavaScript following functional core with imperative shell architecture.

Core Principles

File Structure Pattern

Copycomponents/
└── my-component/
    ├── my-component.js           # Main component class
    ├── my-component-template.js  # Template function
    ├── my-component-styles.js    # CSS-in-JS styles
    └── my-component-i18n.js      # Translations object

Web Component Template

Copyimport { template } from './my-component-template.js';
import { styles } from './my-component-styles.js';
import { translations } from './my-component-i18n.js';

/**
 * @class MyComponent
 * @extends HTMLElement
 * @description Brief description of component purpose
 * @fires my-component-update - Fired when state changes
 */
class MyComponent extends HTMLElement {
    static get observedAttributes() {
        return ['lang', 'value'];
    }

    constructor() {
        super();
        this.attachShadow({ mode: 'open' });
    }

    // FUNCTIONAL CORE - Pure getters
    get lang() {
        return this.getAttribute('lang') ||
               this.closest('[lang]')?.getAttribute('lang') ||
               document.documentElement.lang ||
               'en';
    }

    get translations() {
        return translations[this.lang] || translations.en;
    }

    // IMPERATIVE SHELL - Side effects
    render() {
        this.shadowRoot.innerHTML = `
            <style>${styles}</style>
            ${template(this.translations)}
        `;
    }

    connectedCallback() {
        this.render();
        // Set up observers and listeners
    }

    disconnectedCallback() {
        // Clean up observers and listeners - REQUIRED
    }

    attributeChangedCallback(name, oldValue, newValue) {
        if (oldValue !== newValue) {
            this.render();
        }
    }
}

customElements.define('my-component', MyComponent);

export { MyComponent };

Quick Reference

ESLint Rules Enforced

Naming Conventions

Related Documentation

• WEB-COMPONENTS.md - Lifecycle and Shadow DOM
• JSDOC.md - Documentation patterns
• I18N.md - Internationalization
• EVENTS.md - Event handling
• ACCESSIBILITY.md - a11y in JavaScript
• DEFENSIVE.md - Type guards, error handling, feature detection

Skills to Consider Before Writing

When authoring JavaScript, consider invoking these related skills:

When Creating Web Components

If your JavaScript file defines a custom element (extends HTMLElement), also invoke:

• custom-elements - For registration patterns, slots, attribute handling
• state-management - If component manages internal state
• accessibility-checker - For keyboard navigation, ARIA

When Making API Calls

If your code uses fetch() or makes network requests:

• api-client - Retry logic, timeout handling, typed responses
• error-handling - Network error recovery, user feedback

Related Skills

• custom-elements - Define and use custom HTML elements
• state-management - Client-side state patterns for Web Components
• api-client - Fetch API patterns with error handling and caching
• data-storage - localStorage, IndexedDB, SQLite WASM patterns
• error-handling - Consistent error handling across frontend and backend
• unit-testing - Write unit tests with Node.js native test runner
• typescript-author - TypeScript for Web Components and Node.js