algorithm-visualizer

An interactive web application that visualizes and compares sorting algorithms side by side in real time.

All algorithms sort the same shuffled dataset at the same playback speed, so you can see how they differ in strategy, comparisons, and data movement.

Key Features

• Bubble sort, selection sort, merge sort, and quick sort each run in their own panel. Each bar is labeled with its value.
• The merge sort panel shows the values remaining on each side, the value just moved to the result, and the result as it is built.
• Use the chips above the playback controls to choose which algorithms to show, and drag the handle beside each chip to reorder the panels. Keyboard users can press Space, move with arrow keys, and press Space to drop or Escape to cancel. Hidden algorithms keep their playback state.
• Play, pause, and shuffle, and set the number of bars (5–50) and the animation speed (0.2×–10×).
• Japanese and English UI (chosen from the browser language, with a manual switch), light and dark modes, and a layout that adapts to the screen width.

Architecture & How It Works

Sorting and playback are separated:

flowchart LR
    Input["Initial Shuffled Array"] --> Gen["Pure Step Generator<br>(build*Steps)"]
    Gen -->|"Array of Step objects<br>(compare, swap, pivot, etc.)"| State["Playback Engine<br>(App State & Timer)"]
    State -->|"Immutable Board State"| UI["React Components<br>(Bar Rendering & Overlays)"]

1. Each algorithm has a pure function in src/plugins/visualizer.ts that sorts a copy of the input and records the whole process as an array of Step objects (compare, swap, write, and so on).
2. src/App.tsx applies one step to each board per tick of the animation timer, without re-running the sort.

Tech Stack

• Framework: React 19, TypeScript
• UI & Styling: Mantine UI, Vanilla CSS
• Bundler & Tooling: Parcel, Vitest, Testing Library, ESLint, Prettier

yarn typecheck runs TypeScript 7 (tsc, installed as @typescript/native). The typescript package is an alias of @typescript/typescript6, which provides the TypeScript 6 API that typescript-eslint needs, because TypeScript 7 does not ship an API yet. This follows Running side-by-side with TypeScript 6.0.

Development Setup

The project is configured to run inside Docker. Node.js on the host is needed only for the pre-commit hook when it runs there (see Pre-commit Hook), and optionally for type resolution in an editor running on the host.

The Node.js version is set in .nvmrc. CI and the production build on Render read it, and the Docker image uses the same major version. Update them together.

Dependencies are managed with Yarn 1 (Classic). The Docker image ships Yarn 1, and in CI Corepack uses its default, Yarn 1, because package.json has no packageManager field. CI installs with yarn install --frozen-lockfile, which fails when package.json has a dependency or version range that yarn.lock does not include. After changing dependencies, update yarn.lock in the container (for example with yarn add or yarn install) and commit it together with package.json.

Using Docker Compose

# Start dev server with hot reload
docker compose up -d --build

The application is served at:

• Japanese: http://localhost:1234/ja/
• English: http://localhost:1234/en/

Each checkout, including each git worktree, runs as its own Compose project with its own container. They all publish host port 1234 by default, though, so only one dev server can use it at a time. To run another checkout's server alongside, pick a different host port with DEV_PORT:

DEV_PORT=1235 docker compose up -d --build

That server is then at http://localhost:1235/ja/ and http://localhost:1235/en/. Pass the same DEV_PORT whenever you run docker compose up again in that checkout; docker compose exec does not need it.

Using Dev Containers

If your editor supports VS Code Dev Containers:

1. Open this repository in your container-supported editor.
2. Select Reopen in Container. Dependencies will be installed automatically.

Quality Checks & Commands

Run commands inside the running container:

# Execute tests
docker compose exec -T app bash -c 'yarn test'

# Type check, lint, format check, and test in one go
docker compose exec -T app bash -c 'yarn typecheck && yarn lint && yarn format && yarn test'

Command	Description
yarn dev	Starts Parcel dev server
yarn build	Builds the production bundle into public/, with asset URLs pointing to the production site so Open Graph images are absolute
yarn typecheck	Validates TypeScript types (tsc --noEmit)
yarn lint / yarn lint:fix	Runs ESLint / applies auto-fixes
yarn format / yarn format:fix	Checks / applies Prettier formatting
yarn test	Runs Vitest unit and UI test suite

Pre-commit Hook

A Husky pre-commit hook runs lint-staged on staged files. It runs inside the app container when that service is running, and on the host otherwise.

In a git worktree, the container mounts only the worktree, so the shared .git directory is not visible inside it. The hook therefore always runs on the host there, which requires host dependencies. Install them with the Node.js version from .nvmrc (for example, after nvm use):

COREPACK_ENABLE_AUTO_PIN=0 yarn install --frozen-lockfile

For the same reason, Husky's prepare script prints a git error during the container's install in a worktree. The error is harmless and does not stop the install.

Project Structure

src/
├── App.tsx                    # Main layout, playback loop, and board states
├── plugins/                   # Step types and step generators (visualizer.ts), i18n setup (i18n.ts)
├── components/                # Shared UI controls, bars, and per-algorithm overlays
│   ├── ControlBar.tsx
│   ├── SortSection.tsx
│   └── algorithms/            # Visual representations & legends for each algorithm
├── ja/, en/                   # Localized HTML templates and dictionary strings
└── __tests__/                 # Logic tests and UI component specifications