CLion 2019.1 Help

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 the NodeJS plugin on the Plugins page as described in Plugins.

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.

Local and Remote debugging

CLion supports two debugging modes:

  • Local debugging: in this mode, your application is started from CLion 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 CLion attaches to a running process. CLion recognizes --inspect and now deprecated --debug flags so you can make any application accessible for remote debugging. To debug a remote application, use an Attach to Node.js/Chrome configuration.

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. If necessary, CLion can generate a JavaScript Debug configuration and start it automatically together with the Node.js configuration.

  3. Select the newly created Node.js configuration from the Select run/debug configuration list on the toolbar and click the Debug button 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 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.

Using interactive Debugger Console

When you are debugging a Node.js application, CLion 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.*.

    Node.js debugging: Console tab
  • In the Debugger Console, you can run JavaScript code snippets and view the console.* messages.

Run JavaScript in the Debugger Console

  1. Start typing a statement at > in the input field. As you type, CLion suggests variants for completion.

  2. Select the relevant statement and press Enter. CLion shows its value in the console.

Navigate to source code

  • At each line with output of console.*, CLion shows the name of the file and the line where it was called. Click this link to jump to the call in the source code.

  • The Debugger Console also shows stack traces. Click the link next to a reported problem to jump to the line of code where this problem occurred.

Filter out messages

The console shows objects in a tree view, with stack traces collapsed by default. Warnings (console.warn()), errors (console.error()), and info (console.info()) messages have different icons and background colors to make them easier to notice.

  • To hide log messages of specific types, click the Filter button and select the severities to filter out.

    Node.js interactive debugger console: filtering out messages by type

Group messages

  • The log messages grouped using console.group() and console.groupEnd() are displayed as a tree. To show the output collapsed by default, use console.groupCollapsed().

    Node.js interactive debugger console: log messages grouped

Apply CSS styles

  • Use CSS and the %c marker to apply styles to log messages.

    Node.js interactive debugger console: applying CSS style to log messages

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 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

  • In the embedded Terminal (Alt+F12), type npm install --save-dev nodemon or yarn add nodemon --dev 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>

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. Select the newly created Attach to Node.js/Chrome configuration from the Select run/debug configuration list on the toolbar and click Debug button 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.

Node.js multiprocess debugging

CLion 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. Select the newly created configuration from the Select run/debug configuration list on the toolbar and click Debug the Debug button.

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

    ws_node_multiprocess.png

    and so on To examine the data (variables, watches, and so on) 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: 2 July 2019

See Also