Node.js — Debugging

console Methods

console.log('Basic log');
console.info('Info');
console.warn('Warning');
console.error('Error');
console.table([{ name: 'John' }, { name: 'Jane' }]);
console.time('timer');
// ... code ...
console.timeEnd('timer');

Node Inspector

node --inspect app.js

Then open chrome://inspect in Chrome.

Debugger Statement

function add(a, b) {
    debugger;  // Execution pauses here
    return a + b;
}

VS Code Debugging

// .vscode/launch.json
{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "node",
            "request": "launch",
            "name": "Launch Program",
            "program": "${workspaceFolder}/app.js"
        }
    ]
}

Debug Module

npm install debug

const debug = require('debug')('app:server');

debug('Server starting on port %d', 3000);

DEBUG=app:* node app.js

Profiling

node --prof app.js
node --prof-process isolate-*.log > processed.txt

Mini Practice

1. Use console methods
2. Debug with --inspect
3. Set up VS Code debugging
4. Use the debug module

Up Next

Continue with Async Programming — async patterns.