LangChain Examples Collection

A comprehensive collection of LangChain implementations demonstrating various AI integration patterns, from basic prompts to advanced multi-stage pipelines.

Quick Start

npm init -y
npm install langchain @langchain/core @langchain/google-genai @langchain/ollama dotenv

Create .env file:

GOOGLE_API_KEY=your-google-api-key

Chain Examples

Basic Implementations

• chain.js - Simple prompt template with Google GenAI (docs)
• chain2.js - Direct message handling with dotenv integration (docs)
• chain3.js - Streaming translation with command-line arguments (docs)
• chain4.js - String output parsing for clean responses (docs)
• chain5.js - Basic PromptTemplate formatting (no AI model) (docs)

Advanced Features

• chain6.js - Multimodal image analysis with base64 encoding (docs)
• chain7.js - Pipeline prompt composition for movie recommendations (docs)
• chain8.js - Local Ollama integration (no API keys needed) (docs)
• chain9.js - Callback monitoring and token usage tracking (docs)
• chain10.js - Request cancellation with abort signals (docs)

Output Parsing & Data Structures

• chain11.js - String and comma-separated list parsers (docs)
• chain12.js - JSON output parsing with RunnableSequence (docs)
• chain13.js - Multi-stage chain composition (Ollama) (docs)
• chain13g.js - Multi-stage chain composition (Google GenAI) (docs)

Key Concepts Demonstrated

• Basic Prompting: Template variables and model invocation
• Streaming Responses: Real-time output processing
• Local vs Cloud: Ollama vs Google GenAI comparison
• Output Parsing: String, JSON, and list data extraction
• Chain Composition: Multi-stage processing pipelines
• Error Handling: Timeouts, cancellation, and graceful failures
• Multimodal: Text + image processing capabilities

Running Examples

# Google GenAI examples (require API key)
node chain.js
node chain2.js
node chain3.js "Hello world!" "Spanish"

# Local Ollama examples (require Ollama service)
ollama pull gemma3:4b-it-qat
node chain8.js
node chain11.js

# Advanced features
node chain6.js  # Image analysis
node chain9.js  # Usage tracking
node chain10.js # Cancellation demo

Documentation

Detailed specifications available in docs/specs/ directory:

• Each chain has corresponding documentation explaining architecture and usage
• Examples include code patterns, configuration options, and best practices

Dependencies

• @langchain/core - Core LangChain functionality
• @langchain/google-genai - Google Generative AI integration
• @langchain/ollama - Local Ollama model integration
• dotenv - Environment variable management