loto/docs/code-standards.md

Code Standards

File Naming & Structure

• Kebab-case for all files: PlayerBoard.svelte, game-logic.js.
• Descriptive names: Long names are preferred for self-documentation. Avoid ambiguity.
• Single responsibility: Each file has one primary export (component or utilities).
• Max 200 lines per file: Split larger components into smaller focused ones.

Svelte 5 Runes & JavaScript

Rune Globals & eslint

Svelte 5 runes ($state, $derived, $effect, $props, $bindable, $inspect, $host) are declared as readonly globals in eslint.config.mjs (lines 16–22) to suppress "undefined variable" linter errors. They are usable in .svelte and .svelte.js files without import.

State & Reactivity

• $state: For mutable local UI state (grid, crossed, booleans). let grid = $state(...)
• $derived: For computed values that auto-update when dependencies change. const rowCompleteness = $derived(grid && crossed.length ? [...] : [])
• $effect: For side effects (localStorage sync, detecting completed rows). Replaces React useEffect.
• $props: For destructuring component props. let { storagePrefix = "loto" } = $props()

Reactive Store Files (.svelte.js)

Use the .svelte.js extension for modules that export rune-based reactive state (e.g., settings-store.svelte.js). This signals to bundlers and linters that the file uses Svelte 5 reactivity at module scope.

Plain References (No Reactivity)

• Use regular let or const for timers, Sets, Maps (not reactive). Example: let toastTimer = null; const celebratedRows = new Set();

Typing (JSDoc)

• Use JSDoc @typedef {Object} for prop types, JSDoc type annotations for functions.
• jsconfig.json has checkJs: false (not enabled), so types are documentation-only.
• Component props: @typedef {Object} Props { ... } then /** @type {Props} */ let { ... } = $props()
• Avoid any; use precise types (e.g., number[][] for grid).
• Generics: @template T for utility functions.

Client-Only Architecture

• SvelteKit's ssr: false in +layout.js disables server rendering.
• All pages are client-only; no server-side data fetching.
• Use localStorage exclusively for persistence.

CSS & Tailwind 4 Patterns

Utilities

• Utility-first: className="px-4 py-2 rounded-lg text-white".
• Responsive: sm:, md:, lg: prefixes for breakpoints.
• Dark mode: dark:bg-slate-800, dark:text-white.
• Animations: Custom keyframes in globals.css, apply via animate-fade-in.

Layout

• Flexbox for alignment: flex flex-col items-center justify-center.
• Grid for game boards: .loto-grid { grid-template-columns: repeat(9, 1fr); }.
• Aspect ratio for square cells: aspect-square.

Gradients

• Player page: from-indigo-500 to-purple-500.
• Host page: from-orange-500 to-red-500.
• Completed rows: bg-emerald-100 + text-emerald-500.
• Shadows: shadow-lg shadow-indigo-500/25.

localStorage Patterns

Saving

/**
 * @param {number[][]} grid
 * @param {string} [prefix]
 */
function saveGrid(grid, prefix = "loto") {
  localStorage.setItem(`${prefix}_grid`, JSON.stringify(grid));
}

Loading

/**
 * @param {string} [prefix]
 * @returns {number[][] | null}
 */
function loadGrid(prefix = "loto") {
  const data = localStorage.getItem(`${prefix}_grid`);
  if (!data) return null;
  try {
    return JSON.parse(data);
  } catch {
    return null;
  }
}

Key Pattern: {prefix}_{key} enables multiple independent boards per component reuse.

Error Handling

• Silent fallback: JSON parse errors return null; caller checks for null.
• No try-catch in render: Keep logic in $effect or event handlers.
• Confirmation dialogs: confirm("Bạn có muốn...") for destructive actions.

Naming Conventions

Pattern	Example	Usage
camelCase	handleCellClick, storagePrefix	variables, functions, props
PascalCase	PlayerBoard, MasterPage	components, types
UPPER_SNAKE	STORAGE_KEY, NUM_ROWS	constants
kebab-case	PlayerBoard.svelte	file names

Comment Style

• Document why, not what. The code shows what it does.
• Use /** JSDoc */ for exported functions.
• Inline comments for complex logic (e.g., weighted random selection in src/lib/game-logic.js:19–28).

Example

/**
 * Weighted random selection of a column index.
 * @param {number[]} weights
 * @returns {number}
 */
function randomANumberInRow(weights) {
  // Convert weights to cumulative distribution for O(n) lookup
  const tempWeight = [...weights];
  for (let i = 1; i < tempWeight.length; i++) {
    tempWeight[i] += tempWeight[i - 1];
  }
  // ...
}

Internal Navigation

• Use import { base } from '$app/paths' for internal links to preserve basePath across deployments.
• Example: <a href="{base}/master">Host page</a> works on root ("") and subpath (/loto) equally.

Import Organization

1. SvelteKit imports ($app/paths, $lib/...)
2. Third-party imports
3. Local component/utility imports

import { base } from "$app/paths";
import { generateGrid, isRowComplete } from "$lib/game-logic.js";
import PlayerBoard from "$lib/PlayerBoard.svelte";

Component Patterns

Props Pattern

<script>
  /**
   * @typedef {Object} Props
   * @property {string} [storagePrefix]
   */
  /** @type {Props} */
  let { storagePrefix = "loto" } = $props();
</script>

Event Handlers

Use inline event handlers (onclick, onkeydown). Svelte 5 handles click delegation. Event objects automatically passed:

<button onclick={() => handleCellClick(row, col)}>Click</button>
<div onkeydown={(e) => e.key === "Escape" && dismiss()}>Dialog</div>

Testing

Unit Tests (Implemented)

• Framework: Vitest 4.1.5 with happy-dom
• Test Files: src/lib/game-logic.test.js (26 tests), src/lib/settings-store.test.js (12 tests) — 38 total passing
• Coverage: Game logic (generateGrid shape/constraints, isRowComplete, getWaitingNumber, persistence with validators), settings (load/save/reset with error handling)
• Scripts: npm test (run once), npm run test:watch (continuous)
• Pattern: Use vitest's describe / it blocks, expect() assertions. Test both happy path and error cases (corrupt JSON, missing localStorage).

Component Tests (Planned)

Future: render PlayerBoard, mock localStorage, verify toast/popup behaviors.

E2E Tests (Planned)

Future: Playwright for player flow (generate → click → bingo) and host flow (draw → master board updates).

Configuration

Environment Variables (code-server only)

• VITE_DEV_PROFILE: "codeserver" triggers proxy config.
• CODESERVER_HOST: Hostname for HMR.
• CODESERVER_PORT: Port (defaults to 3000).

Set in .env.local (not committed).

Build Targets

• adapter-static: Generates static HTML + JS in build/.
• basePath: Dual-mode: "" (Cloudflare, dev) or /loto (GitHub Pages via BUILD_PROFILE=gh).

Last reviewed: 2026-04-27