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  1. Web Development
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  3. Running and debugging Node.js

Running and debugging Node.js

Last modified: 17 November 2022

Available only in PyCharm Professional: download to try or compare editions

Required plugins:

Javascript and TypeScript, JavaScript Debugger, Node.js -  The plugins are available only in PyCharm Professional, where they are enabled by default.

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

Before you start

Running a Node.js application

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

Create a Node.js run/debug configuration

warning

Do not set up a working directory for the default Run/Debug Configurations listed under the Templates node. This may lead to unresolved targets in newly created Run/Debug Configurations.

  1. From the main menu, select Run | Edit Configurations. Alternatively, select Edit Configurations from the list on the toolbar.

    Open the Edit Configurations dialog

    In the Edit Configurations dialog that opens, click the Add button (the Add button) on the toolbar and select Node.js from the list. The Run/Debug Configuration: Node.js dialog opens.

  2. Specify the Node.js interpreter to use.

    If you choose the Project alias, PyCharm will automatically use the project default interpreter from the Node interpreter field on the Node.js page . In most cases, PyCharm detects the project default interpreter and fills in the field itself.

    You can also choose another configured local or remote interpreter or click the Browse button and configure a new one.

  3. 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).

  4. 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.

    • In the Application parameters field, specify the Node.js-specific arguments to be passed to the application on start through the process.argv array.

    • To open the application in the browser automatically, configure a before-launch task. Click App general arrow right to expand the Before launch area, click the Add button, and select Launch Web Browser from the list. In the dialog that opens, specify the URL of the application starting page, for example, localhost:3000 for Express applications, and the browser to use.

      Before-launch task: open browser
      Before-launch task: open browser

Run an application

  • Select the newly created Node.js configuration from the Select run/debug configuration list on the toolbar and click the Run button (the Run button) next to the list.

    Start an app with a run/debug configuration

    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

  1. Create a Node.js run/debug configuration as described above and go to the Logs tab.

  2. Click the Add button next to the Log files to be shown in console field which lists the available log files (if any).

  3. 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.

  4. 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.

  5. 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

PyCharm 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 PyCharm attaches to a running process.

    PyCharm 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 PyCharm, 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

https://resources.jetbrains.com/help/img/idea/2022.3/ws_node_debug-local.png
Gif

Debugging a running Node.js application

With PyCharm, 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.

https://resources.jetbrains.com/help/img/idea/2022.3/ws_node_debug_attach_from_terminal.png
Gif

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.

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.

Debugging a Node.js application that uses nodemon

tip

See Running and debugging scripts for details.

The PyCharm 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

  1. Set the breakpoints in your code as necessary.

  2. 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.

    Attach no Node.js run configuration: 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.

    Node.js application with nodemon running in the debug mode: check the port

  3. Select the newly created Attach to Node.js/Chrome configuration from the Select run/debug configuration list on the toolbar and click the Debug button (the Debug button) next to the list. The debugger stops at the breakpoints that you put in your code in PyCharm.

    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.

See also

Procedures

Reference