Debug JavaScript in Chrome

Last modified: 11 October 2024

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

Required plugins:

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

PyCharm 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 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 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

PyCharm has a built-in web server that can be used to preview and debug your application in a web browser or IDE's 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>. PyCharm 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 the program execution, examine it when suspended, view actual HTML DOM, run JavaScript code snippets in the Console, 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 PyCharm to start with your user data. For more information, refer to Starting a debugging session with your default Chrome user data.

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

PyCharm 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 () 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.cn/help/img/idea/2024.2/ws_js_debug_reload_in_browser.png
Gif

Debug an application that is 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 (), from the Run tool window, or from the Debug tool window. Just hold and click the URL at which the application is running.

https://resources.jetbrains.com.cn/help/img/idea/2024.2/ws_js_start_debugging_from_run_tool_window.png
Gif

  1. Set the breakpoints in your code.

  2. Start the application in the development mode, for example, using an npm script.

  3. The Run tool window or the Terminal shows the URL at which your application is running. Hold and click this URL link. PyCharm starts a debugging session with an automatically generated configuration of the type JavaScript Debug.

This also works for debugging Vue.js, Angular, React, and Node.js applications.

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 PyCharm, 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:/PyCharmProjects/MyProject and the web server document root is C:/XAMPP/htdocs, for PyCharm this web server is remote.

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

To debug an application on a remote web server, you need to have the copies of its sources in a PyCharm project. To synchronize local and remote sources, create a deployment configuration as described in Create a remote server configuration and Connect to a 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 Connect to a 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 the program execution, examine it when suspended, view actual HTML DOM, run JavaScript code snippets in the Console, 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 PyCharm 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.

  1. Let's now deploy our simple application to a local web server , refer to Deploy. In the following example, it is Apache:

    Debug JavaScript on an external web server: uploaded sources on the remote host

  2. When using a local web server, such as Nginx or Apache, as in our example, or the web server is on a remote host, you need to create a Run/Debug configuration to start the JavaScript debugger. To do that, click the list at the upper right-hand corner of the PyCharm window and choose Edit Configurations. Alternatively, choose Run | Edit Configurations from the main menu:

    Debug JavaScript on an external web server: open Edit configurations dialog

    In the Run/Debug Configurations dialog, click and choose JavaScript Debug from the list:

    Create JavaScript 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.

    Specify the URL of your running application, in our example it is http://localhost:8888/MySimpleApp/index.html

    URL to run your application

    In our example, the local project structure and the file structure on the server are the same so no mappings are required.

  3. Now we can start debugging: choose the new run/debug configuration from the list in the upper right-hand corner of the PyCharm window, and then click the Debug button:

    Editor, main menu and the toolbar

    In the Debug tool window, proceed as usual: step through the program, stop and resume the program execution, examine it when suspended, view actual HTML DOM, run JavaScript code snippets in the Console, and so on.

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.

PyCharm 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

PyCharm supports debugging asynchronous client-side JavaScript code. PyCharm 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. PyCharm displays a full call stack, including the caller and the entire way to the beginning of the asynchronous actions.

https://resources.jetbrains.com.cn/help/img/idea/2024.2/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

PyCharm supports debugging Service Workers and Web Workers. PyCharm 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 PyCharm can debug only dedicated workers, debugging for shared workers is currently not supported.

See also

Procedures

Reference

Tutorials and Examples