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Chat CLI (Stage 1)

A simple command-line chat application demonstrating module organization

Overview​

This example builds on Hello World by organizing code into multiple files with clear responsibilities. You'll see how to structure a real project and persist data to disk.

Why this matters:

  • Demonstrates module separation (storage, messages, display)
  • Shows the I/O/P model in a practical application
  • Introduces file-based persistence
  • Prepares you for multi-file web applications

What You'll Learn​

  • Module Separation: Breaking code into logical files
  • Persistence: Saving messages to a local JSON file
  • CLI Interaction: Parsing command-line arguments
  • I/O/P Model Applied:
    • Input: Command line arguments
    • Processing: Creating message objects with timestamps
    • Output: Console display and file storage

Prerequisites​

Project Structure​

11-chat-cli/
├── package.json
├── README.md
└── src/
    ├── index.js      # Entry point, CLI argument parsing
    ├── messages.js   # Message creation and formatting
    ├── storage.js    # File persistence (JSON)
    ├── display.js    # Console output formatting
    └── users.js      # User identification

Quick Start​

cd examples/11-chat-cli

# Send a message
npm start send "Hello DevFoundry!"

# Read message history
npm start read

# Get help
npm start help

Key Concepts​

1. Module Boundaries​

Each file has a single responsibility:

FileResponsibility
index.jsParse arguments, orchestrate flow
messages.jsCreate and format message objects
storage.jsRead/write to messages.json
display.jsFormat output for console
users.jsIdentify current user

2. Business Logic is Separate from I/O​

The messages.js module contains pure business logic — it doesn't know about files or the console. This same logic will work unchanged in the browser version.

3. Data Persistence​

Messages are stored in a JSON file, demonstrating how applications maintain state between runs.

Ask Better Questions (Use AI as a Guide)​

When exploring this project, try asking your AI assistant specific questions that reference real files:

  • "What does the createMessage function in src/messages.js return, and why does it include a timestamp?"
  • "In src/index.js, how does the app decide whether to run send or read?"
  • "How does src/storage.js make sure existing messages aren't lost when a new one is saved?"

Specific questions that name a file and a behavior get far better answers than vague ones. For a ready-made template you can copy and adapt, see the Reading Code prompt guide.

Curriculum Alignment​

This example aligns with:

  • Module 02: Anatomy of a Project — Understanding multi-file structure
  • Module 04: Types as Communication — Message shape as a contract

Next Steps​

Ready to see the same logic in a browser? Continue to Chat Static Web.

Source Code​

View the complete source: examples/11-chat-cli/