How to Debug Node.js Code in VS Code with Breakpoints

// Keyboard shortcuts
// Open Run & Debug panel:  Ctrl+Shift+D  (Cmd+Shift+D on Mac)
// Start debugging:         F5
// Stop debugging:          Shift+F5
// Step over (next line):   F10
// Step into (go inside):   F11
// Step out (go up):        Shift+F11
// Continue to breakpoint:  F5 (while paused)

// .vscode/launch.json
{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "node",
            "request": "launch",
            "name": "Launch Program",
            "skipFiles": ["<node_internals>/**"],
            "program": "${workspaceFolder}/src/index.js"
            // For TypeScript with ts-node:
            // "program": "${workspaceFolder}/src/index.ts",
            // "runtimeArgs": ["-r", "ts-node/register"]
        }
    ]
}

// Example: src/index.js
// Set a breakpoint on line 12 by clicking the gutter

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

app.get('/users/:id', async (req, res) => {
    const userId = parseInt(req.params.id);   // <- breakpoint here
    const user = await getUserById(userId);

    if (!user) {
        return res.status(404).json({ error: 'Not found' });
    }

    res.json(user);
});

// When paused at a breakpoint:
// - Hover over any variable to see its value in a tooltip
// - In the Watch panel, add expressions like:
//     user.email
//     req.headers['authorization']
//     Array.isArray(results)
//     results.length > 0

// The Debug Console (bottom panel) lets you run arbitrary code
// in the paused context — great for one-off inspections:
// > user
// > Object.keys(req.body)
// > new Date(user.created_at).toISOString()

// Typical stepping workflow:
// 1. F5  → start; pauses at first breakpoint
// 2. F10 → step over to next line, inspect variables
// 3. F11 → step INTO getUserById() to see what happens inside
// 4. F10 → step through lines inside getUserById()
// 5. Shift+F11 → step OUT back to the calling function
// 6. F5  → continue to next breakpoint or program end

// Use F10 most of the time.
// Use F11 only when you need to go inside a specific function.
// Use Shift+F11 to get out of a utility function quickly.

// Right-click the breakpoint → Edit Breakpoint → Expression

// Pause only when i equals 500
// Expression: i === 500

// Pause only when user is null
// Expression: user === null

// Pause when a specific ID is processed
// Expression: req.params.id === '42'

// Hit Count: pause every N times the line is hit
// (separate option in the same menu)
// Useful for: pause every 100th iteration

// Enable Auto Attach:
// Ctrl+Shift+P → "Debug: Toggle Auto Attach" → Smart

// Then in the integrated terminal:
node src/index.js
// VS Code automatically attaches — breakpoints are active

// Works with npm scripts too:
npm run dev
// As long as the underlying process is Node.js, it attaches

// Works with nodemon:
nodemon src/index.js
// Each restart re-attaches automatically

// 1. Start Node with the inspector
node --inspect src/index.js
// Listening on ws://127.0.0.1:9229/...

// Or for immediate pause on first line:
node --inspect-brk src/index.js

// 2. Add to .vscode/launch.json
{
    "type": "node",
    "request": "attach",
    "name": "Attach to Running Node",
    "port": 9229,
    "skipFiles": ["<node_internals>/**"]
}

// 3. In VS Code: F5 → select "Attach to Running Node"
// Breakpoints activate immediately