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Overview

The possibility to debug JavaScript is vital for the web developers. With IntelliJ IDEA-based products, such debugging becomes quite easy. To illustrate the JavaScript debugging capabilities with PyCharm, we’ll create a very basic script that just shows some numbers in a browser page, and then debug it on a server.

In case of debugging on an external web server, the application files are deployed on it, and you have their copies on your computer. No matter, whether the web server itself is running on a physically remote host or on your machine, application files deployed on it are treated as remote.

When a remote HTML file with a JavaScript injection is opened, the debugger tells PyCharm the name of the currently processed file and the number of the line to be processed. PyCharm opens the local copy of this file and indicates the line with the provided number. This behaviour is enabled by specifying correspondence between files and folders on the server and their local copies. This correspondence is called mapping, it is set in the debug configuration.

Before you start

Make sure that:

  • You are working with PyCharm Professional Edition version 3.0 or higher.
  • You are working with Google Chrome (this tutorial is written for Chrome).
  • You have JetBrains IDE Support extension installed and activated. If you launch the debugger for the very first time, PyCharm will warn you about the necessity to install the extension JetBrains IDE Support.
    For example, with Chrome, you can tell that JetBrains extension is installed and activated, when icon shows to the right of the address bar, and it is non-transparent.
    You can install JetBrains IDE Support extension yourself.
  • You are using XAMPP as an application server (this tutorial is written for XAMPP).

Creating a simple project

On the main menu, choose File→New Project, choose the empty project type, and specify the name MyJSProject:

Choose to open this new project in a separate window, not adding it to any of the currently open projects:

Preparing an example

First, let’s create a HTML page. To do that, with the Project tool window having the focus, press Alt+Insert, choose HTML file on the pop-up menu, and enter the file name numbers:

PyCharm stubs out an HTML file with some initial contents. Next, embed a reference to a JavaScript file into this HTML file. To do that, type the following code inside the <body> tags:

Mind the code completion, which is available while you type:

When ready, pay attention to the highlighted file name numbers.js. This is a reference to a non-existent JavaScript file. Place the caret at this name and press Alt+Enter (or click the yellow light bulb ); a quick fix is suggested – create the missing file:

Choose this quick fix, and have the stub JavaScript file ready. Next, enter the following code:

Setting breakpoints

Now let’s set breakpoints to our JavaScript file. This is most easy – just click the left gutter at the line you want the script to suspend:

Configuring a server

Creating a server

To do that, open Settings/Preferences dialog (press Ctrl+Alt+S or click on the main toolbar), in the Deployment page click and specify the server name MyRemoteServer and type local or mounted server.

Configuring connection and mappings

Then, configure the server. In the Connection tab, specify the directory where your local files will be uploaded; in our case, this directory is C:\xampp\htdocs - it means that the local files will be uploaded to this directory:

Click the Mappings tab. Here define the local path, the deployment path on the server (which is relative to the folder specified in the Connection tab), and the Web path on the server:

Defining project default server

Make the server the project default. To do that, click button in the Deployment toolbar.

Viewing the server

Let's make sure the server is up and running, and, which is even more important, visible to PyCharm. To do that, on the main menu, choose Tools → Deployment → Browse Remote Hosts. The Remote Hosts tool window shows the newly created server:

Deploying files to the server

With PyCharm, it's just a snap... For example, you can easily do that via the main menu: choose Tools → Deployment → Upload to MyRemoteServer, and make sure that the new directory C:\xampp\htdocs is created on the server.

Another approach is to use the context menus of the files: both contain same command Upload to MyRemoteServer.

Debugging

Starting the debugger session

All the preliminary steps are done, and it’s time to proceed to the debugging session. To start it, right-click the background of the file numbers.html, and choose Debug 'number.html' on the context menu - thus you will launch the debugger with the default temporary run/debug configuration:

Examining the debugger information

When the debugging session is launched, your HTML page appears in the browser, and the Debug tool window opens. Your program execution suspends when the first breakpoint is hit. Such a breakpoint is marked with a blue stripe:

To learn about the behavior of the breakpoints, refer to the tutorial Breakpoints and to the product documentation.

As you step through your application, the corresponding information appears in the Debug tool window, and in the page of your web browser:

To step though the script, click or ; to terminate the debugger session, close the yellow banner, or click Cancel.

See also

Running and debugging JavaScript

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