This tutorial will guide you through using the Anthropic API with Node.js to interact with Claude models programmatically.

Prerequisites

• Node.js 14+
• npm or yarn
• An Anthropic API key (obtain from https://console.anthropic.com/)

Installation

npm install @anthropic-ai/sdk
# or using yarn
yarn add @anthropic-ai/sdk

Basic Usage

1. Setting Up

First, import the Anthropic client and set up your API key:

const Anthropic = require('@anthropic-ai/sdk');
// Or using ES modules:
// import Anthropic from '@anthropic-ai/sdk';

const anthropic = new Anthropic({
  apiKey: 'your-api-key-here', // Replace with your actual API key
});

2. Sending a Basic Message

async function sendMessage() {
  try {
    const message = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      max_tokens: 1000,
      messages: [
        { role: 'user', content: 'What is the capital of France?' }
      ]
    });
    
    console.log(message.content);
  } catch (error) {
    console.error('Error:', error);
  }
}

sendMessage();

3. Having a Multi-turn Conversation

async function haveConversation() {
  try {
    const conversation = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      max_tokens: 1000,
      messages: [
        { role: 'user', content: 'What is machine learning?' },
        { role: 'assistant', content: 'Machine learning is a subset of artificial intelligence...' },
        { role: 'user', content: 'Can you give me an example?' }
      ]
    });
    
    console.log(conversation.content);
  } catch (error) {
    console.error('Error:', error);
  }
}

Advanced Features

1. System Prompts

Using system prompts to set context and behavior:

async function useSystemPrompt() {
  try {
    const response = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      system: 'You are a helpful math tutor who explains concepts step by step.',
      messages: [
        { role: 'user', content: 'Explain how to solve quadratic equations' }
      ]
    });
    
    console.log(response.content);
  } catch (error) {
    console.error('Error:', error);
  }
}

2. Handling Stream Responses

For real-time streaming responses:

async function streamResponse() {
  try {
    const stream = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      max_tokens: 1000,
      messages: [{ role: 'user', content: 'Write a story about a space adventure' }],
      stream: true
    });

    for await (const chunk of stream) {
      if (chunk.type === 'content_block_delta') {
        process.stdout.write(chunk.delta.text);
      }
    }
  } catch (error) {
    console.error('Error:', error);
  }
}

3. Error Handling with Express.js

const express = require('express');
const app = express();

app.post('/ask-claude', async (req, res) => {
  try {
    const response = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      messages: [{ role: 'user', content: req.body.question }]
    });
    
    res.json({ answer: response.content });
  } catch (error) {
    if (error instanceof Anthropic.APIError) {
      res.status(500).json({ error: 'API Error', details: error.message });
    } else if (error instanceof Anthropic.RateLimitError) {
      res.status(429).json({ error: 'Rate limit exceeded' });
    } else {
      res.status(500).json({ error: 'Unexpected error' });
    }
  }
});

Best Practices

1. Environment Variables Using dotenv for API key management:

// Install dotenv: npm install dotenv
require('dotenv').config();

const anthropic = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY
});

2. Rate Limiting and Retries Using axios-retry for automatic retries:

const axiosRetry = require('axios-retry');
const axios = require('axios');

// Configure retry behavior
axiosRetry(axios, { 
  retries: 3,
  retryDelay: axiosRetry.exponentialDelay,
  retryCondition: (error) => {
    return axiosRetry.isNetworkOrIdempotentRequestError(error) ||
           error.response?.status === 429;
  }
});

3. Async/Await Wrapper Utility function for cleaner error handling:

const asyncHandler = (fn) => (req, res, next) => {
  return Promise.resolve(fn(req, res, next)).catch(next);
};

// Usage in Express
app.post('/ask-claude', asyncHandler(async (req, res) => {
  const response = await anthropic.messages.create({
    model: 'claude-3-opus-20240229',
    messages: [{ role: 'user', content: req.body.question }]
  });
  res.json({ answer: response.content });
}));

Common Use Cases

1. Content Generation API

const express = require('express');
const router = express.Router();

router.post('/generate-blog', async (req, res) => {
  try {
    const { topic } = req.body;
    const response = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      messages: [
        { role: 'user', content: `Write a blog post about ${topic}` }
      ]
    });
    
    res.json({ blogPost: response.content });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

2. Text Analysis Service

class TextAnalysisService {
  constructor(anthropicClient) {
    this.anthropic = anthropicClient;
  }

  async analyzeSentiment(text) {
    const response = await this.anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      messages: [
        { role: 'user', content: `Analyze the sentiment of this text: ${text}` }
      ]
    });
    return response.content;
  }
}

module.exports = TextAnalysisService;

Example Express.js Application

const express = require('express');
const Anthropic = require('@anthropic-ai/sdk');
require('dotenv').config();

const app = express();
app.use(express.json());

const anthropic = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY
});

app.post('/chat', async (req, res) => {
  try {
    const response = await anthropic.messages.create({
      model: 'claude-3-opus-20240229',
      messages: req.body.messages
    });
    res.json(response);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Resources

• Official Documentation
• API Reference
• Node.js SDK Documentation

Remember to always check the official documentation for the most up-to-date information and best practices.