Claude Code: Claude Code First Use

# 1. Create a practice project
mkdir my-first-claude && cd my-first-claude
git init

# 2. Create a simple file
echo 'function hello() { return "Hello"; }' > index.js

# 3. Launch Claude Code
claude

╭─────────────────────────────────────────╮
│  Claude Code                             │
│  Model: claude-sonnet-4-20250514         │
│  Project: my-first-claude                │
╰─────────────────────────────────────────╯

> █ (type your instruction)

> Hello, please look at this project

Claude: Let me check the project structure and file contents...

  📁 Project structure:
  - index.js

  📄 index.js:
  ```javascript
  function hello() { return "Hello"; }

---

## 3. Operation Confirmation Mechanism

### (1) Permission Approval Flow

Claude Code requests confirmation for sensitive operations:

| Operation Type | Default Behavior | Example |
|:--------------|:----------------|:--------|
| **Read file** | Auto-execute | Read index.js |
| **Create file** | Request confirmation | Create new file test.js |
| **Modify file** | Request confirmation | Modify existing file |
| **Run command** | Request confirmation | Execute npm test |
| **Delete file** | Request confirmation | Delete old file |

### (2) Confirmation Options

```text
Claude wants to edit index.js:
  - Add goodbye() function after hello()
  - Add module.exports

  Allow? (y/n/a/e)
  y = yes (this time)
  n = no
  a = always allow edits to this file
  e = edit the change before applying

> Refactor project to TypeScript

Claude: I'll perform the following:
  1. Create tsconfig.json
  2. Convert index.js to index.ts
  3. Add type definitions
  4. Update package.json

  Allow creating tsconfig.json? [y/n/a/e] y
  ✅ Created tsconfig.json

  Allow editing index.js → index.ts? [y/n/a/e] a
  ✅ Always allowing edits to index.ts

  Allow running: npm install typescript --save-dev? [y/n/a/e] y
  ✅ Installed typescript

  All changes applied successfully!

# View current session file changes
claude /diff

# View git diff
git diff

# View specific file changes
git diff index.js

# Revert all changes (git-based)
git checkout .
git clean -fd

# Revert single file
git checkout -- index.js

# View change history
git log --oneline -5

> Rename all functions

Claude: Renaming functions...
  → hello → greet
  → goodbye → farewell
  → Modified 3 files

# Alice finds the rename doesn't match expectations
# Use git to revert

$ git diff --stat
  index.js       | 6 +++---
  index.test.js  | 8 ++++----
  utils.js       | 4 ++--

$ git checkout .
# All changes reverted ✓

# Bad description
> Help me change some code

# Good description
> In src/auth/jwt.ts, add token refresh logic,
> set expiry to 7 days, write corresponding unit tests

# Better description (with constraints)
> Refactor UserService query methods:
> 1. Use Repository pattern instead of direct SQL
> 2. Add pagination support (default 20 per page)
> 3. Write integration tests
> 4. Don't modify the interface signatures

# Alice's first Claude Code experience

# 1. Prepare project
mkdir todo-app && cd todo-app
git init
npm init -y

# 2. Launch Claude Code
claude "Create a simple Node.js TODO app:
1. Support add, delete, list tasks
2. Store data in JSON file
3. Include complete unit tests
4. Use ES Module syntax"

# Claude Code work process:
# → Reading package.json
# → Creating src/todo.js (core TODO logic)
# → Creating src/storage.js (JSON file storage)
# → Creating src/index.js (CLI entry)
# → Creating tests/todo.test.js (unit tests)
# → Running: npm test → 8/8 passed ✓
# → Creating README.md

# 3. Check results
git add -A && git commit -m "feat: initial todo app by Claude Code"

# 4. Add more requirements
claude "Add task priority feature (high/medium/low), update tests"

# Claude Code continues iterating...