How to Use Debugger in Node.js: Simple Guide

To use the debugger in Node.js, start your script with node inspect yourfile.js or add the --inspect flag to enable debugging with Chrome DevTools. You can also insert the debugger statement in your code to pause execution and inspect variables.

Syntax

Use node inspect yourfile.js to start the built-in debugger in the terminal. Alternatively, use node --inspect yourfile.js to enable debugging via Chrome DevTools. Insert debugger; in your code where you want to pause execution.

• node inspect yourfile.js: Runs the debugger in the terminal.
• node --inspect yourfile.js: Opens a debugging port for Chrome DevTools.
• debugger;: Pauses execution at this line when debugger is active.

bash

node inspect yourfile.js

// or

node --inspect yourfile.js

// In your JavaScript code:
debugger;

Example

This example shows how to use the debugger statement to pause execution and inspect variables using the terminal debugger.

javascript

function add(a, b) {
  const sum = a + b;
  debugger;
  return sum;
}

console.log('Result:', add(5, 3));

Output

Breakpoint 1 set in add at line 3
> 1 (function add(a, b) {
  2   const sum = a + b;
  3   debugger;
  4   return sum;
  5 })
debug> n
> 4 (  return sum;)
debug> n
Result: 8
debug> c

Common Pitfalls

Common mistakes include forgetting to start Node.js with the inspect flag, which disables debugging, or placing debugger statements where they never get executed. Also, some developers try to use node inspect but expect Chrome DevTools to open automatically, which requires the --inspect flag instead.

Always ensure your Node.js version supports the --inspect flag (Node.js 8+).

javascript

/* Wrong way: debugger statement without starting with inspect */
function test() {
  debugger;
  console.log('Hello');
}
test();

/* Right way: start with inspect flag */
// Run in terminal:
// node --inspect yourfile.js

Quick Reference

Command/Concept	Description
node inspect yourfile.js	Start debugger in terminal mode
node --inspect yourfile.js	Enable debugging with Chrome DevTools
debugger;	Pause execution at this line when debugging
chrome://inspect	URL to open Chrome DevTools for Node.js debugging
n (next)	Step to next line in terminal debugger
c (continue)	Continue execution until next breakpoint

Key Takeaways

Start Node.js with --inspect flag to debug using Chrome DevTools.

Use the debugger statement in code to pause execution at desired points.

node inspect runs the debugger in the terminal but does not open DevTools.

Ensure your Node.js version supports the inspect flag (Node.js 8+).

Use Chrome's chrome://inspect page to connect to Node.js debugging sessions.