Running and debugging Node.js

CLion helps you run and debug your Node.js applications. You can debug applications that are started from CLion as well as attach to already running applications.

Before you start

Install and enable the Node.js plugin on the Settings/Preferences | Plugins page, tab Marketplace, as described in Installing plugins from JetBrains repository.

Running a Node.js application

CLion runs Node.js applications according to a run configuration of the type Node.js. CLion also uses this configuration to start the debugger together with Node.js applications.

Create a Node.js run/debug configuration

From the main menu, choose Run | Edit Configuration, then in the Edit Configurations dialog, click on the toolbar and select Node.js from the list. The Run/Debug Configuration: Node.js dialog opens.
Specify the Node.js interpreter to use. If you choose the Project alias, CLion will automatically use the project default interpreter from the Node interpreter field on the Node.js and NPM page.
In most cases, CLion detects the project default interpreter and fills in the field itself. You can also choose another configured local interpreter or click and configure a new one.
In the JavaScript File field, specify the path to the main file of the application that starts it (for example, bin/www for Express applications).
Optionally:
- Specify the Node Parameters that customize the start of Node.js. For example, you may want to enable an experimental Node.js feature or pass another option, see the Node.js official website for details.
  The default debugger port is 5858.
- In the Application parameters field, specify the Node.js-specific arguments to be passed to the application on start through the process.argv array.

Run an application

Select the newly created Node.js configuration from the Select run/debug configuration list on the toolbar and click next to it. The application starts, and the Run tool window opens showing the application output.

If you are using a logging tool like morgan in your application and this tool writes logs to a file, you can see these logs in the Console tab of the Run tool window.

Manage logs when running a Node.js application

Create a Node.js run/debug configuration and go to the Logs tab.
Click next to the Log files to be shown in console field which lists the available log files (if any).
In the Edit Log Files Aliases dialog that opens, type the alias name to show in the list of log entries and specify the location of the log file. Select whether you want to show all files that this pattern covers or only the last one.
Click OK to return to Node.js Run/Debug Configuration dialog, where the new log file is added to the list. Select the Is Active checkbox next to it. To skip the previous content, select the Skip Content checkbox.
Optionally:
- To enable saving the Process Console output to a log file, select the Save console output to file checkbox and specify the file location.
- Choose when you want the Process Console shown.

Debugging a Node.js application

CLion makes it easier to debug Node.js applications. You can put breakpoints right in your JavaScript or TypeScript code so you no longer need any debugger and console.log() statements. You can do many things that will help you explore the code and understand where the bug is. In the Debug tool window, you can view the call stack and the variables in their current state, evaluate expressions in the editor, and step through the code.

You can initiate a debugging session in two ways:

Start the debugger together with your application using a Node.js run/debug configuration.
Attach the debugger to an already running application. In this case, your application is already running in the debug mode and CLion attaches to a running process.
CLion recognizes --inspect, --inspect-brk, and now deprecated --debug flags so you can make any application accessible for debugging.
To debug a running application, use an Attach to Node.js/Chrome configuration.

Starting the debugger together with a Node.js application on your computer

Set the breakpoints in the code where necessary.
Create a Node.js run/debug configuration. If necessary, CLion can generate a JavaScript Debug configuration and start it automatically together with the Node.js configuration.
Select the newly created Node.js configuration from the Select run/debug configuration list on the toolbar and click next to it. The Debug tool window opens.
Perform the steps that will trigger the execution of the code with the breakpoints.
Switch to CLion, where the controls of the Debug tool window are now enabled. Proceed with the debugging session — step through the breakpoints, switch between frames, change values on-the-fly, examine a suspended program, evaluate expressions, and set watches.

Debugging a Node.js application that uses nodemon

The CLion built-in debugger can automatically reconnect to running Node.js processes. This lets you debug Node.js applications that use the nodemon utility, which automatically reloads your Node.js process when the code is updated.

To debug such application, you need to start it in the debug mode (with the --inspect or --inspect-brk flag) and then connect to it using the Attach to a Node.js/Chrome debug configuration with the Reconnect Automatically option on.

Install nodemon

In the embedded Terminal(Alt+F12), type npm install --save-dev nodemon or yarn add nodemon --dev to install nodemon as a development dependency.

Start an application with nodemon in the debug mode

Create and run the following npm debug script:
debug": "nodemon --inspect <path_to_the_file_that_starts_your_application>
See Running and debugging scripts for details.

Debug an application

Set the breakpoints in your code as necessary.
Create a new Attach to a Node.js/Chrome configuration as described in Debugging a running Node.js application and select the Reconnect automatically checkbox.

Usually, you don’t need to change the port in the configuration 9229 because it’s the default port the debugger is listening on. But you can double-check what port is used in the message logged when you run the app in the debug mode.
Select the newly created Attach to Node.js/Chrome configuration from the Select run/debug configuration list on the toolbar and click next to it. The debugger stops at the breakpoints that you put in your code in CLion.
Now, every time you make any changes to the code and save them Ctrl+S, nodemon will automatically reload the application and the debugger will automatically re-attach to the restarted process.

Last modified: 16 July 2021