Debugging Node.js Applications: Tools and Techniques

Master debugging Node.js applications with this guide. Learn how to use the Core Node.js Debugger, Node Inspector, and built-in IDE debuggers. Includes examples and step-by-step instructions.

Debug Node.js Application

Learn how to debug Node.js applications using various tools:

  • Core Node.js Debugger
  • Node Inspector
  • Built-in Debugger in IDEs

Core Node.js Debugger

Node.js provides a built-in non-graphic debugger for all platforms. Here’s how to use it:

Consider the following Node.js application in app.js:

Syntax

var fs = require('fs');

fs.readFile('test.txt', 'utf8', function (err, data) {
    debugger; // Pause execution here
    if (err) throw err;
    console.log(data);
});

Add debugger; where you want the execution to pause. To start debugging, run:

Syntax

node inspect app.js

This command starts the debugger and pauses at the first debugger; statement.

Commands to use during debugging:

  • next: Move to the next statement.
  • cont: Continue to the next debugger; statement.
  • step: Step into a function.
  • out: Step out of a function.
  • watch('expression'): Watch a variable or expression.
  • watchers: Show values of watched expressions.
  • pause: Pause running code.
Syntax

watch('data'); // Watch the 'data' variable

To check the value of all watched variables, use the watchers command.

Additional debugging tips:

  • Logging: Use console.log for basic output.
  • Debugger Statements: Use debugger; to pause execution.
  • Inspecting Variables: Use the inspect command to examine variables.
  • Profiling: Use Node’s profiler to find performance issues.

Alternative Debugging Tools

Other popular debugging tools include:

  • Node Inspector: A GUI-based debugger built on Chrome DevTools.
  • Visual Studio Code: Includes a built-in debugger.
  • Other IDEs: WebStorm, IntelliJ IDEA, Eclipse, etc.

Best Practices

  • Test Thoroughly: Write comprehensive tests to catch issues early.
  • Logging: Implement robust logging for production.
  • Error Handling: Gracefully handle errors to prevent crashes.
  • Performance Optimization: Profile your app to identify bottlenecks.

In the next section, learn how to use Node Inspector to debug Node.js applications.