PyCharm 2018.2 Help

Running and Debugging Node.js

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

Install and enable the NodeJS plugin. The plugin is not bundled with PyCharm, but it can be installed from the JetBrains plugin repository as described in Managing Plugins.

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 for debugging Node.js applications locally.

To create a Node.js run/debug configuration

  1. From the main menu, choose Run | Edit Configuration, then in the Edit Configurations dialog, click icons general add on the toolbar and select Node.js from the pop-up list. The Run/Debug Configuration: Node.js dialog opens.
  2. Specify the Node.js interpreter to use. This can be a local Node.js interpreter or a Node.js on Windows Subsystem for Linux.
  3. In the JavaScript File field, specify the path to the main file of the application that starts it (for example, bin/www for Node.js Express applications).
  4. Optionally:
    • Specify the Node Parameters that customize the start of Node.js. For example, to make your application accessible for remote debugging, type one of the debugging flags depending on your Node.js version: --inspect=<debugger port> for Node.js versions 6.5 and higher or --debug=<debugger port> for any Node.js version earlier than 8. The default debugger port is 5858.
    • In the Application parameters text box, specify the Node.js-specific arguments to be passed to the application on start through the process.argv array.

To run an application

  • Choose the newly created Node.js configuration in the Select run/debug configuration drop-down list on the toolbar and click icons toolwindows toolWindowRun svg 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.

To 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 icons general add svg 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 console output to a log file, select the Save console output to file checkbox and specify the file location.
    • Choose when you want the Console shown.
    Node.js run/debug configuration: Log tab

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.

Local and Remote debugging

PyCharm supports two debugging modes:

  • Local debugging: in this mode, your application is started from PyCharm and is running locally on your computer. To debug it, use a Node.js configuration.
  • Debugging a remote application: in this mode, your application is running in a remote environment in the debug mode and PyCharm attaches to a running process. PyCharm recognizes --inspect and --debug flags so you can make any application accessible for remote debugging. PyCharm supports remote debugging with the Chrome Debugging Protocol and the V8 Debugging Protocol (also known as Legacy Protocol). In either case, a debugging session is initiated through a run/debug configuration of the type Attach to Node.js/Chrome.

Debugging a Node.js application locally

  1. Set the breakpoints in the Node.js code where necessary.
  2. Create a Node.js run/debug configuration as described above. If necessary, PyCharm can generate a JavaScript Debug configuration and start it automatically together with the Node.js configuration as described in Starting a JavaScript Debug configuration together with a Node.js configuration.
  3. Choose the newly created Node.js configuration in the Select run/debug configuration drop-down list on the toolbar and click icons actions startDebugger svg next to it. The Debug Tool Window opens.
  4. Perform the steps that will trigger the execution of the code with the breakpoints.
  5. Switch to PyCharm, 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.

Using interactive Debugger Console

When you are debugging a Node.js application, PyCharm shows two console tabs in the Debug tool window - Console and Debugger Console.

  • The Console tab shows the output of the node process itself, that is, everything that is written to process.stdout and process.stderr directly or is logged using console.*.
    ws_node_debugging_process_console.png
  • The Debugger Console lets you execute JavaScript code, view the console.log messages, jump to the location where console.log was called, and use other console features provided by the Chrome Debugging Protocol.
    ws_node_debugging_debug_console.png

Debugging a running Node.js application

With PyCharm, you can debug an application that is running in a remote environment. PyCharm supports remote debugging with the Chrome Debugging Protocol and 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.

To debug with Chrome Debugging Protocol

  1. Set the breakpoints as necessary.
  2. Choose Run | Edit Configurations from the main menu, then click icons general add svg in the Edit Configuration dialog box that opens, and choose Attach to Node.js/Chrome from the list. The Run/Debug Configuration: Attach to Node.js/Chrome dialog box opens.
  3. Specify the host where the target application is running and the port passed to --inspect 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.
  4. In the Attach to area, choose Chrome or Node.js > 6.3 started with --inspect.
  5. Choose the newly created Attach to Node.js/Chrome configuration in the Select run/debug configuration drop-down list on the toolbar and click icons actions startDebugger svg next to it. The Debug Tool Window opens.
  6. Perform the actions that will trigger the code at the breakpoint. Control over the debugging session returns to PyCharm.
  7. Switch to PyCharm. 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.

To debug with V8 Debugging Protocol

  1. 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.
  2. Make sure the application to debug has been launched in the remote environment with the following parameters: --debug=<debugger port>. The default port is 5858.
  3. Proceed as during a debugging session with Chrome Debugging Protocol.

Debugging a Node.js application that uses nodemon

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 flag) and then connect to it using the Attach to a Node.js/Chrome debug configuration with the Reconnect Automatically option on.

To install nodemon

  • Open the embedded Terminal (View | Tool Windows | Terminal or Alt+F12) and type npm install --save-dev nodemon or yarn add nodemon --dev at the command prompt to install nodemon as a development dependency.

To 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>
  • Alternatively, pass the inspect flag through a Node.js run/debug configuration as described above.

To 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. Choose the newly created Attach to Node.js/Chrome configuration in the Select run/debug configuration drop-down list on the toolbar and click Debug button next to it. 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.

Starting a JavaScript Debug configuration together with a Node.js configuration

With PyCharm, you can debug the server-side code and the client-side JavaScript code of your application in two modes:

  • Separately, using single-run configurations.
  • Simultaneously, using a complex Node.js with JavaScript Debug configuration. All you need is configure the behaviour of the browser and enable debugging the client-side code of the application. This functionality is provided through a JavaScript Debug run configuration, so technically, PyCharm creates separate run configurations for the server-side and the client-side code, but you specify all your settings in one dedicated Node.js run configuration.

To create a compound Node.js/JavaScript Debug configuration

  1. Choose Run | Edit Configuration on the main menu.
  2. From the list, choose the Node.js run configuration to start together with a JavaScript Debug configuration. In the dialog box that opens, switch to the Browser / Live Edit tab.
  3. Select After launch to start a browser automatically when you launch a debugging session.
  4. In the text box below, type the URL address to open the application at.
  5. Choose the browser to use from the drop-down list next to the After launch checkbox.
    • To use the system default browser, choose Default.
    • To use a custom browser, choose it from the list. Note that Live Edit is fully supported only in Chrome.
    • To configure browsers, click Browse browseButton and adjust the settings in the Web Browsers dialog box that opens. For more information, see Configuring Browsers.
  6. Select With JavaScript debugger.
As for any other JavaScript debugging session, you can enable the Live Edit functionality as described in Live_Editing.

To enable Live Edit in a Node.js application

  1. Make sure the LiveEdit repository plugin is installed and enabled. The plugin is not bundled with PyCharm, but it can be installed from the JetBrains plugin repository as described in Managing Plugins.
  2. In the Settings/Preferences dialog (Ctrl+Alt+S), click Debugger under Build, Execution, Deployment, and then click Live Edit. The Live Edit page opens.
  3. Select Update Node.js application on changes. Set the elapsed time for applying the changes to a running application: accept the default value 300 ms or specify a custom value using the spin box next to the corresponding field.

Debugging a Node.js application running in a remote environment

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

Debugging a Node.js application in a Docker container

PyCharm supports debugging of Node.js applications in Docker containers through run/debug configurations of the type Node.js.

Before you start debugging a Node.js application on Docker

  1. Make sure Docker is installed, configured, and running.

To choose the Node.js interpreter on Docker

  1. Create a Node.js run/debug configuration as described above.
  2. Select one of the configured Node.js interpreters of the type Remote Interpreter - Docker from the drop-down list or configure a new one.

To specify the Docker container settings

  • Click browseButton next to the Edit Docker Container Settings field and specify the settings in the Edit Docker Container Settings dialog that opens.
    Alternatively, select the Auto configure checkbox to do it automatically. Learn more about the Auto configure mode at Quick Tour of WebStorm and Docker: What Happens On Each Run.

To configure port bindings

  1. Click browseButton next to the Docker Container Settings field.
  2. In the Edit Docker Container Settings dialog that opens, expand the Port bindings area.
  3. Click icons general add svg and in the Port bindings dialog that opens, map the ports as follows:
    • In the Container port text box, type the port specified in your application.
    • In the Host port text box, type the port through which you want to open the application in the browser from your computer.
    • In the Host IP text box, type the IP address of the Docker's host, the default IP is 192.168.99.100. The host is specified in the API URL field on the Docker page of the Settings / Preferences Dialog.
    • Click OK to return to the Edit Docker Container Settings dialog where the new port mapping is added to the list.
  4. Click OK to return to the Run/Debug Configuration: Node.js dialog.

To start debugging

  1. Set the breakpoints in the Node.js code as necessary.
  2. Choose the newly created Node.js configuration in the Select run/debug configuration drop-down list on the toolbar and click icons actions startDebugger svg next to it.
  3. Proceed as during a local debugging session, as described above.

Node.js multiprocess debugging

PyCharm supports debugging additional Node.js processes that are launched by the child_process.fork() method or by the cluster module. Such processes are shown as threads in the Frame pane on the Debugger tab of the Debug Tool Window.

  1. Set the breakpoints in the processes to debug.
  2. Create a Node.js run/debug configuration.
  3. Choose the newly created configuration in the Select run/debug configuration drop-down list on the tool bar and click Debug icons actions startDebugger svg.

    The Debug Tool Window opens and the Frames drop-down list shows the additional processes as threads as soon as they are launched:

    ws_node_multiprocess.png

    To examine the data (variables, watches, etc.) for a process, select its thread in the list and view its data in the Variables and Watches panes. When you select another process, the contents of the panes are updated accordingly.

Last modified: 17 August 2018

See Also