Debugging Node.js Applications: Using the Built-in Debugger
Learn how to effectively debug your Node.js applications using the built-in debugger. This tutorial explains how to start the debugger, use common debugging commands (continue, next, step, pause), inspect variables, and troubleshoot your JavaScript code.
Debugging Node.js Applications
Introduction
Node.js includes a built-in debugger that uses a simple TCP-based protocol. This debugger allows you to step through your JavaScript code, inspect variables, and identify errors. This tutorial explains how to use the Node.js debugger.
Starting the Debugger
To start the debugger, use the `node debug` command followed by the name of your JavaScript file:
Starting the Debugger
node debug script.js
Replace `script.js` with the actual path to your JavaScript file. If you omit the filename, the debugger will start in interactive mode, prompting for commands.
Example
To debug a file named `main.js`, you would run:
Debugging main.js
node debug main.js
Handling Errors
If you provide an incorrect file path or have errors in your JavaScript code, the debugger will output error messages. For example, if `main.js` isn't in the current directory or contains syntax errors, the output would indicate the problem.
Debugger Commands
Common Node.js Debugger Commands
The Node.js debugger provides a set of commands to control the flow of execution and inspect the state of the application. Below is a list of common debugger commands along with a brief explanation of what each command does:
| Command | Description |
|---|---|
| cont | Resumes the execution of the program until the next breakpoint is hit. It continues the process without stepping into any functions. |
| next | Steps over the current line of code. If the line contains a function call, it will execute the function without stepping into it. |
| step | Steps into the current line of code. If the line contains a function call, it will enter the function and pause execution at the first line inside it. |
| backtrace | Displays the stack trace of the current execution, showing the function calls that led to the current point in the code. |
| repl | Opens an interactive Read-Eval-Print Loop (REPL) where you can run JavaScript code in the current context, allowing you to inspect variables and experiment with code. |
| quit | Exits the debugger and terminates the debugging session. |
Conclusion
The built-in Node.js debugger is a valuable tool for identifying and fixing errors in your JavaScript code. It provides a simple way to interact with your running application during debugging.