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Debug JavaScript in Chrome

Last modified: 06 April 2025

Required plugins:

Javascript and TypeScript, JavaScript Debugger  -  The plugins are bundled with CLion and enabled by default.

CLion provides a built-in debugger for your client-side JavaScript code.

note

Debugging of JavaScript code is only supported in Google Chrome and in other Chromium-based browsers.

Before you start

  1. Make sure the JavaScript and TypeScript bundled plugin is enabled in the settings. Press CtrlAlt0S to open settings and then select Plugins. Click the Installed tab. In the search field, type JavaScript and TypeScript. For more information about plugins, refer to Managing plugins.

  2. Make sure the JavaScript Debugger bundled plugin is enabled in the settings. Press CtrlAlt0S to open settings and then select Plugins. Click the Installed tab. In the search field, type JavaScript Debugger. For more information about plugins, refer to Managing plugins.

  3. Configure the built-in debugger as described in Configuring JavaScript debugger.

    To have the changes you make to your HTML, CSS, or JavaScript code immediately shown in the browser without reloading the page, activate the Live Edit functionality. For more information about the live editing functionality, refer to Live Edit in HTML, CSS, and JavaScript.

Debug an application that is running on the built-in server

CLion has a built-in web server that can be used to debug your application in a web browser or preview your code in the CLion built-in browser. This server is always running and does not require any manual configuration.

Start debugging

  1. Set the breakpoints in the JavaScript code, as required.

  2. Open the HTML file that references the JavaScript to debug or select the HTML file in the Project tool window.

  3. From the context menu of the editor or the selection, choose Debug <HTML_file_name>. CLion generates a debug configuration and starts a debugging session through it. The file opens in the browser, and the Debug tool window appears.

    tip

    To save the automatically generated configuration for further re-use, choose Save <HTML_file_name> from the context menu after the debugging session is over.

  4. In the Debug tool window, proceed as usual: step through the program, stop and resume program execution, examine it when suspended, explore the call stack and variables, set watches, evaluate variables, view actual HTML DOM, and so on.

Example

Let's suppose that you have a simple application that consists of an index.html file and an index.js file, where index.html references index.js.

To start debugging this application using the built-in server, set a breakpoint in index .js, open index .html in the editor, and select Debug 'index.html' from the context menu.

Start debugging session from the editor

CLion creates a run/debug configuration automatically, and a debugging session starts.

Debugging session starts, the app opens in the browser

To restart the new run/debug configuration, select it from the list and click the Debug button.

Restart debugging session

Reload the current page in browser

Besides restarting your application by clicking the Rerun button (the Rerun button) in the Debug tool window, you can also use the Reload in Browser action to reload the page where you have currently navigated. This works the same way as the Reload Page functionality (Ctrl0R) in Chrome.

  • To reload the current page, click the More icon on the toolbar and select Reload in Browser (Reload in Browser).

    Reload in Browser action

The example below shows a simple application that consists of two HTML pages and a JavaScript script. The starting home.html page has a Submit button on pressing which the calculator.html page opens with the results of the Calculator.js script execution.

During a debugging session, clicking the Rerun button (the Rerun button) reloads the home.html page with the Submit button. Clicking the Reload in Browser button (the Reload in Browser button) reloads the calculator.html page so all the previous script output is cleared and the debugger returns to line 1 in Calculator.js.

https://resources.jetbrains.com/help/img/idea/2025.1/ws_js_debug_reload_in_browser.png
Gif

Debug an application running on the localhost in the development mode

If your application is running in the development mode on localhost, you can start debugging it from the built-in Terminal (AltF12), from the Run tool window, or from the Debug tool window. Just hold CtrlShift and click the URL at which the application is running.

Debug an application that is running on a remote web server

Often you may want to debug client-side JavaScript of an application that is running on an external development web server.

What is a remote web server?

In CLion, any server with the document root outside the current project is called remote. This server may be actually running on a physically remote host or on your machine.

For example, if your project is in C:/CLionProjects/MyProject and the web server document root is C:/XAMPP/htdocs, for CLion this web server is remote.

How do I synchronize my application sources on the server with their local copies in my CLion project?

To debug an application on a remote web server, you need to have the copies of its sources in a CLion project. To synchronize local and remote sources, create a deployment configuration as described in Remote server configuration and Synchronization with web server.

Debug an application on a remote web server

  1. Set the breakpoints in the JavaScript code, as required.

  2. Create a run/debug configuration of the JavaScript Debug type:

    Go to Run | Edit Configurations, then in the Edit Configurations dialog, in the Edit Configurations dialog that opens, click the Add button (the Add button) on the toolbar and select JavaScript Debug from the list.

  3. In the Run/Debug Configuration: JavaScript Debug dialog that opens, specify the URL address at which the application is running. This URL address should be a concatenation of the Web server root URL and the path to the HTML file relative to the web server document root in accordance with server access configuration. For more information, refer to Synchronization with web server.

    Click OK to save the configuration settings.

  4. Choose the newly created configuration in the Select run/debug configuration list on the toolbar and click the Debug button Start the debugger. The HTML file specified in the run configuration opens in the chosen browser and the Debug tool window appears.

  5. In the Debug tool window, proceed as usual: step through the program, stop and resume program execution, examine it when suspended, explore the call stack and variables, set watches, evaluate variables, view actual HTML DOM, and so on.

tip

By default, a debugging session starts in a new window with a custom Chrome user data. To open a new Chrome instance with your familiar look-and-feel, configure Chrome in CLion to start with your user data. For more information, refer to Starting a debugging session with your default Chrome user data.

Example: Debug without mappings

Suppose you have a simple application that consists of an index.html file and an App.js file, where index.html references App.js.

Mappings

Mappings set correspondence between files on a web server and their local copies. You need mappings:

  • When your application is deployed and running on a remote web server.

  • When you have defined several resource root folders in addition to the project root.

CLion attempts to guess path mappings from the deployment configuration or based on file and script names and content. However, if your application structure is complicated, you need to specify path mappings manually.

Configure mappings

  1. Create a debug configuration of the type JavaScript Debug as described in Debugging an application.

  2. In the Remote URLs of local files area, map the files and folders to URL addresses of files and folders on the server according to the currently used deployment configuration, see Mapping local folders to folders on the server and the URL addresses to access them.

Example: Debug with mappings

Suppose that for some reason you decide to change the folder structure of the application from the previous example and move index.html and App.js to a separate folder src.

The structure of local folders differs from the folder structure on the remote web server

Because the local sources and the application on the web server are structured differently, the debugger will be unable to sync the local sources with the code that is actually executed.

To solve the problem, let's map the URL address of the application root with the src folder.

For more debugging examples, refer to the following posts in the WebStorm blog: Debugging React Applications and Debugging Angular Applications.

Debug asynchronous code

CLion supports debugging asynchronous client-side JavaScript code. CLion recognizes breakpoints inside asynchronous code, stops at them, and lets you step into such code. As soon as a breakpoint inside an asynchronous function is hit or you step into asynchronous code, a new element Async call from <caller> is added in the Frames pane of the Debugger tab. CLion displays a full call stack, including the caller and the entire way to the beginning of the asynchronous actions.

https://resources.jetbrains.com/help/img/idea/2025.1/ws_debug_tool_window_async.png
Gif

In the example above, the debugger stops at line3(breakpoint), then at line5(breakpoint). On clicking Step into, the debugger will stop at line5 (on function), then will move to line6.

The asynchronous debugging mode is turned on by default. To disable asynchronous stack traces, set js.debugger.async.call.stack.depth in Registry to 0.

Debug workers

CLion supports debugging Service Workers and Web Workers. CLion recognizes breakpoints in each worker and shows the debug data for it as a separate thread in the Frames pane on the Debugger tab of the Debug tool window.

Note that CLion can debug only dedicated workers, debugging for shared workers is currently not supported.

Debug Chrome extensions

You can debug Chrome extensions in CLion using a run/debug configuration of the type Attach to Node.js/Chrome. Note that you have to start Chrome with your custom Chrome user data profile, learn more from Start a debugging session with your default Chrome user data.

Create an Attach to Node.js/Chrome run/debug configuration

  1. Go to Run | Edit Configurations. Alternatively, select Edit Configurations from the Run widget 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 Attach to Node.js/Chrome from the list.

    Select the Attach to Node.js /Chrome configuration type

    The Run/Debug Configuration: Attach to Node.js/Chrome dialog opens.

  2. Specify the configuration name and accept the predefined host and port values localhost:9229.

    note

    If you specify a custom port, make sure you specify it later when running Chrome from the command line.

    Create an Attach to Node.js/Chrome run/debug configuration

  3. Click Apply and OK to save the configuration and leave the dialog.

Run Chrome and load the extension

  1. Run Chrome from the command line to specify the remote debugging port and your Chrome user data directory.

    Open the embedded Terminal (AltF12) and type:

    <path_to_chrome_executable> --remote-debugging-port=<port_specified_in_run_configuration> --user-data-dir=<your_Chrome_user_data_directory>

    note

    The predefined port is 9229.

  2. Load your unpacked extension to the Chrome window that opens.

Start debugging

  1. Set the breakpoints where necessary.

  2. From the Run widget list on the toolbar, select the newly created Attach to Node.js/Chrome configuration and click the Debug button next to it.

    Select the Attach to Node.js/Chrome configuration

    The Debug tool window opens.

  3. Go to the Chrome tab where your extension is loaded.

  4. Switch to CLion. 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.

See also

Procedures

Reference