Claude Code JS

A JavaScript SDK for integrating with Claude Code, Anthropic's official CLI tool for Claude.

Overview

This project provides a JavaScript/TypeScript SDK that allows developers to programmatically interact with Claude Code, enabling AI-powered software engineering capabilities in their applications.

Installation

npm install claude-code-js

or with yarn:

yarn add claude-code-js

Quick Start

Basic Setup

import { ClaudeCode } from 'claude-code-js';

// Initialize the SDK
const claude = new ClaudeCode({
  apiKey: process.env.CLAUDE_API_KEY, // Optional: if already logged in
  model: 'claude-3-sonnet', // Optional: specify model
  workingDirectory: './my-project', // Optional: set working directory
  verbose: false // Optional: enable verbose logging
});

Example Usage

Single Chat with Claude

// Send a chat message to Claude with a prompt
const response = await claude.chat({
  prompt: 'Explain this error: TypeError: Cannot read property of undefined',
  systemPrompt: 'You are a helpful coding assistant', // Optional
  appendSystemPrompt: 'Keep explanations concise' // Optional
});

if (response.success) {
  console.log('Result:', response.message.result);
  console.log('Session ID:', response.message.session_id);
  console.log('Cost:', response.message.cost_usd);
} else {
  console.error('Error:', response.error.message);
}

Run Commands Through Claude

// Have Claude execute a task
const result = await claude.runCommand('Fix the failing tests in src/utils.test.js');

if (result.success) {
  console.log('Claude completed the task');
  console.log('Result:', result.message.result);
  console.log('Duration:', result.message.duration_ms, 'ms');
}

Sessions for Multi-turn Conversations

// Create a new session for ongoing conversations
const session = claude.newSession();

// Start the conversation
const firstMessage = await session.prompt({
  prompt: 'What is 2 + 2?',
  systemPrompt: 'You are expert at math. Always return a single line of text in format: equation = result'
});
console.log('First response:', firstMessage.result);

// Continue the conversation
const secondMessage = await session.prompt({
  prompt: '3 + 3 = 6'
});
console.log('Second response:', secondMessage.result);

// Ask for history
const history = await session.prompt({
  prompt: 'Send the history of all validations you have done so far'
});
console.log('History:', history.result);

// Session tracks all messages and session IDs
console.log('Total messages:', session.messages.length);
console.log('All session IDs:', session.sessionIds);

Direct Command Execution

import { executeCommand, streamCommand } from 'claude-code-js';

// Execute a command and get the full output
const { stdout, stderr, exitCode } = await executeCommand(['npm', 'test'], {
  cwd: './my-project',
  timeout: 30000
});

// Stream command output in real-time
const stream = streamCommand(['npm', 'run', 'dev'], {
  onStdout: (data) => console.log('Output:', data),
  onStderr: (data) => console.error('Error:', data)
});

// Wait for completion
await stream;

Real-World Examples

Code Review Assistant

const claude = new ClaudeCode();

// Create a code review session
const reviewer = claude.newSession();

// Start the review
const initialReview = await reviewer.prompt({
  prompt: `Review this Express route for security issues:
    app.post('/login', (req, res) => {
      const { username, password } = req.body;
      const user = db.query('SELECT * FROM users WHERE username = "' + username + '"');
      if (user && user.password === password) {
        res.json({ token: jwt.sign({ id: user.id }, 'secret') });
      }
    })`,
  systemPrompt: 'You are a security-focused code reviewer. Identify vulnerabilities and suggest fixes.'
});

console.log('Initial review:', initialReview.result);

// Ask for specific improvements
const improvements = await reviewer.prompt({
  prompt: 'Show me how to fix the SQL injection vulnerability'
});
console.log('Improved code:', improvements.result);

Test Generator

const claude = new ClaudeCode({ workingDirectory: './my-app' });

// Generate tests for a specific function
const response = await claude.chat({
  prompt: `Generate Jest unit tests for this function:
    export function calculateDiscount(price, discountPercent) {
      if (discountPercent < 0 || discountPercent > 100) {
        throw new Error('Invalid discount percentage');
      }
      return price * (1 - discountPercent / 100);
    }`,
  systemPrompt: 'Generate comprehensive Jest tests with edge cases'
});

if (response.success) {
  // Save the generated tests
  await writeFile('./tests/calculateDiscount.test.js', response.message.result);
}

Interactive Debugging Helper

const debugSession = claude.newSession();

// Start the debugging session
await debugSession.prompt({
  prompt: 'I have a React component that re-renders infinitely. Help me debug it.',
  systemPrompt: 'You are a React debugging expert. Ask clarifying questions and provide solutions.'
});

// Provide more context
await debugSession.prompt({
  prompt: `Here's my component:
    function UserList() {
      const [users, setUsers] = useState([]);
      const fetchUsers = async () => {
        const data = await api.getUsers();
        setUsers(data);
      };
      fetchUsers();
      return <div>{users.map(u => <div>{u.name}</div>)}</div>;
    }`
});

// Get step-by-step debugging guidance
const solution = await debugSession.prompt({
  prompt: `What's causing the infinite re-render and how do I fix it?`
});

Advanced Usage

Working with Multiple Sessions

const claude = new ClaudeCode();

// Create independent sessions for different tasks
const codeReviewSession = claude.newSession();
const debugSession = claude.newSession();

// Start the code review session
await codeReviewSession.prompt({
  prompt: 'Review this code for best practices: function getData() { return fetch("/api").then(r => r.json()) }',
  systemPrompt: 'You are a code reviewer focused on best practices and performance'
});

// Start the debugging session
await debugSession.prompt({
  prompt: 'Help me debug this error: ReferenceError: user is not defined',
  systemPrompt: 'You are a debugging expert'
});

// Continue conversations independently
await codeReviewSession.prompt({ prompt: 'How can I add error handling?' });
await debugSession.prompt({ prompt: 'The error occurs in line 45 of auth.js' });

Chaining Sessions

// Use output from one session as input to another
const mathSession = claude.newSession();
const mathResult = await mathSession.prompt({
  prompt: 'Calculate 15 * 23',
  systemPrompt: 'You are a math expert. Return only the numeric result.'
});

const validationSession = claude.newSession();
const validationResult = await validationSession.prompt({
  prompt: mathResult.result,
  systemPrompt: 'You are expert at validating math calculations.'
});

console.log('Validation result:', validationResult.result);

Session Forking and Reverting

Fork Sessions for Parallel Explorations

The fork() method creates a new session with the same conversation history, allowing you to explore different conversation branches without affecting the original session.

const claude = new ClaudeCode();
const mainSession = claude.newSession();

// Start a conversation
await mainSession.prompt({
  prompt: 'Write a function to calculate factorial',
  systemPrompt: 'You are a helpful coding assistant'
});

await mainSession.prompt({
  prompt: 'Now make it recursive'
});

// Fork the session to explore a different approach
const iterativeSession = mainSession.fork();
const recursiveSession = mainSession.fork();

// Explore iterative approach in one fork
await iterativeSession.prompt({
  prompt: 'Actually, show me an iterative version instead'
});

// Explore memoized approach in another fork
await recursiveSession.prompt({
  prompt: 'Can you add memoization to the recursive version?'
});

// Original session remains unchanged
console.log('Main session messages:', mainSession.messages.length); // 2
console.log('Iterative fork messages:', iterativeSession.messages.length); // 3
console.log('Recursive fork messages:', recursiveSession.messages.length); // 3

Revert Session State

The revert() method removes the most recent messages and session IDs, allowing you to "undo" conversation turns.

const session = claude.newSession();

// Build up a conversation
await session.prompt({ prompt: 'Write a Python hello world' });
await session.prompt({ prompt: 'Now add a loop that prints it 5 times' });
await session.prompt({ prompt: 'Add error handling' });

console.log('Messages before revert:', session.messages.length); // 3

// Revert the last message
session.revert();
console.log('Messages after single revert:', session.messages.length); // 2

// Revert multiple messages at once
session.revert(2);
console.log('Messages after reverting 2:', session.messages.length); // 0

// Continue from the reverted state
await session.prompt({ prompt: 'Write a JavaScript hello world instead' });

Real-World Use Case: A/B Testing Code Solutions

const claude = new ClaudeCode();
const session = claude.newSession();

// Set up the problem
await session.prompt({
  prompt: 'I need to process a large CSV file with millions of rows. What approach should I use?',
  systemPrompt: 'You are an expert in data processing and performance optimization'
});

// Fork to explore different solutions
const streamingFork = session.fork();
const chunkingFork = session.fork();
const parallelFork = session.fork();

// Explore streaming approach
const streamingSolution = await streamingFork.prompt({
  prompt: 'Show me how to implement this using Node.js streams'
});

// Explore chunking approach
const chunkingSolution = await chunkingFork.prompt({
  prompt: 'Show me how to process this in chunks with a batch size'
});

// Explore parallel processing
const parallelSolution = await parallelFork.prompt({
  prompt: 'Show me how to use worker threads for parallel processing'
});

// Compare solutions
console.log('Streaming approach:', streamingSolution.result);
console.log('Chunking approach:', chunkingSolution.result);
console.log('Parallel approach:', parallelSolution.result);

// Pick the best approach and continue
await parallelFork.prompt({
  prompt: 'Add progress tracking to this implementation'
});

Configuration Management

// Update configuration on the fly
claude.setOptions({
  model: 'claude-3-opus',
  verbose: true
});

// Get current configuration
const options = claude.getOptions();
console.log('Current model:', options.model);

Version Checking

// Get the Claude Code CLI version
const version = await claude.version();
console.log('Claude Code CLI version:', version);

Error Handling

try {
  const response = await claude.chat({
    prompt: 'Refactor this function to use async/await'
  });
  
  if (!response.success) {
    // Handle Claude Code specific errors
    console.error(`Error Code: ${response.error.code}`);
    console.error(`Message: ${response.error.message}`);
    
    if (response.error.details) {
      console.error('Details:', response.error.details);
    }
  }
} catch (error) {
  // Handle network or other errors
  console.error('Unexpected error:', error);
}

TypeScript Support

The SDK includes full TypeScript support with exported types:

import { 
  ClaudeCode, 
  ClaudeCodeOptions, 
  ClaudeCodeResponse,
  ClaudeCodeError,
  ClaudeCodeMessage,
  Prompt
} from 'claude-code-js';

// Type-safe configuration
const options: ClaudeCodeOptions = {
  apiKey: process.env.CLAUDE_API_KEY,
  model: 'claude-3-sonnet',
  workingDirectory: './src',
  verbose: true
};

const claude = new ClaudeCode(options);

// Type-safe prompt
const prompt: Prompt = {
  prompt: 'Generate unit tests for auth.js',
  systemPrompt: 'You are a test generation expert',
  appendSystemPrompt: 'Use Jest framework'
};

// Type-safe response handling
const response: ClaudeCodeResponse = await claude.chat(prompt);

if (response.success && response.message) {
  const message: ClaudeCodeMessage = response.message;
  console.log('Result:', message.result);
  console.log('Cost in USD:', message.cost_usd);
  console.log('Duration:', message.duration_ms);
}

Configuration Options

const claude = new ClaudeCode({
  apiKey: 'your-api-key', // Optional: if already logged in via CLI
  model: 'claude-3-sonnet', // Optional: model to use
  workingDirectory: './path/to/project', // Optional: working directory
  verbose: false // Optional: enable verbose output
});

Contributing

We welcome contributions! If you encounter any issues or have ideas for improvements, please don't hesitate to:

• 🐛 Report bugs: Open an issue describing the problem and steps to reproduce
• 💡 Request features: Share your ideas for new functionality
• ❓ Ask questions: Get help with implementation or clarification
• 🔧 Submit PRs: Contribute code improvements or fixes

Opening Issues

Please visit our GitHub Issues page to:

1. Search existing issues to avoid duplicates
2. Use issue templates when available
3. Provide detailed information about your environment and the problem
4. Include code examples when relevant

Support

If you need help or have questions:

1. Check the documentation
2. Search through existing issues
3. Open a new issue with the question tag

License

This project is licensed under the MIT License - see the LICENSE file for details.