Running and debugging Node.js

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

Before you start

Make sure the Node.js plugin is enabled on the Settings/Preferences | Plugins page, tab Installed, see Managing plugins for details.

Running a Node.js application

WebStorm runs Node.js applications according to a run configuration of the type Node.js. WebStorm 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. This can be a local Node.js interpreter or a Node.js on Windows Subsystem for Linux.
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 as described above 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

WebStorm 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 WebStorm attaches to a running process.
WebStorm 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.

With WebStorm, you can also debug Node.js applications that are running in Vagrant boxes, in Docker containers, or on remote hosts accessible via various transfer protocols or via SSH.

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 as described above. If necessary, WebStorm can generate a JavaScript Debug configuration and start it automatically together with the Node.js configuration as described in Debugging the server- and the client-side code.
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 WebStorm, 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 running Node.js application

With WebStorm, you can debug an already running application with the Chrome Debugging Protocol or with the V8 Debugging Protocol (also known as Legacy Protocol).

In either case, a debugging session is initiated through an Attach to Node.js/Chrome configuration.

Start the debugger from the built-in Terminal or from the Run or Debug tool window

If an application was started with the --inspect or --inspect-brk flag, you can start a debugging session from the built-in Terminal, from the Run tool window, or from the Debug tool window.

Attach the debugger to a running app from the built-in Terminal

Run your application with an --inspect or --inspect-brk flag. You can do that in several ways, for example:
- Open the embedded Terminal (Alt+F12) and, type:
  node --inspect-brk <path to the starting page of your application relative to the project root>
- Launch a script from package.json or from the npm tool window, see Run and debug scripts for details.
  
  Depending on the action you select from the list, the output will be shown in the Run or in the Console tab of the Debug tool window.
The Terminal, the Run tool window, or the Console tab of the Debug tool window shows an information message Debugger listening <host>:<port>, the default port is 9229. To start debugging, hold Ctrl+Shift and click the link.
WebStorm starts a debugging session with an automatically generated Attach to Node.js/Chrome configuration.
Alternatively, copy the port number from the Debugger listening <host>:<port> message and paste it later in the Attach to Node.js/Chrome configuration.

Debug with Chrome Debugging Protocol

Use this protocol to debug applications started with the --inspect or --inspect-brk flag. This flag is used with Node.js versions later than 6.3.

Set the breakpoints as necessary.
Select Run | Edit Configurations from the main menu, then click in the Edit Configuration dialog that opens, and select Attach to Node.js/Chrome from the list. The Run/Debug Configuration: Attach to Node.js/Chrome dialog opens.
Specify the host where the target application is running and the port passed to --inspect or --inspect-brk when starting the Node.js process to connect to. Copy the port number from the information message Debugger listening <host>:<port> in the Terminal tool window or in the Run tool window that controls the running application. The default port is 9229.
Optionally: specify the remote paths for the project folders in the Remote URLs of local files area. This is helpful if the root folder of the running application is different from the name of you WebStorm project root folder.
In the Attach to area, select Chrome or Node.js > 6.3 started with --inspect.
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 Debug tool window opens.
Perform the actions that will trigger the code at the breakpoint. Control over the debugging session returns to WebStorm.
Switch to WebStorm. In the Debug tool window, step through the breakpoints, switch between frames, change values on-the-fly, examine a suspended program, evaluate expressions, and set watches.

Debug with V8 Debugging Protocol

Use this protocol to debug applications started with the --debug flag. This flag is used with Node.js versions earlier than 8.

Create an Attach to Node.js/Chrome run/debug configuration as described above and specify the host and the port passed to --debug. The default port is 9229.
Make sure the application to debug was launched with the following parameters: --debug=<debugger port>. The default port is 5858.
Proceed as during a debugging session with Chrome Debugging Protocol.

Debugging a Node.js application that uses nodemon

The WebStorm 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.
Alternatively, pass the inspect flag through a Node.js run/debug configuration as described above.

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 WebStorm.
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