Debugging a Create React App with VS Code · Manorisms

February 09, 2018 0 Comments

Debugging a Create React App with VS Code · Manorisms



In this post (and the above 4 minute embedded video) we’ll look at how to configure Visual Studio Code to debug React Components and Jest Unit Tests inside a web application that was created by create-react-app.

This is the second post in a series about create-react-app. You can start the series with Getting Started with Create React App.

Sample Web Application

Screenshot of Terminal & Empty Browser

On the left, we have a simple playground web application that was previously created with create-react-app.

We can easily kick up a development web server by typing npm start in the terminal. react-scripts will create a new browser tab to the correct URL and port (e.g. http://localhost:3000).

Screenshot of Terminal & Web App

However, our React web application has a bug. If I click on the joke, the answer does not display.

Debugging React Components

By looking at the following code, it may not be obvious what is causing the bug. Wouldn’t it be great if we could debug this code right inside of Visual Studio Code? Well, we can!

Screenshot of Code

  1. Chrome Debugger

    Before we can start debugging, you need to make sure we have the Debugger for Chrome extension installed and reloaded.

    Screenshot of Debugger for Chrome Extension

  2. Making Breakpoints

    Now, we can start making some breakpoints right were we would like to investigate your code.

    Screenshot of Breakpoints

  3. Chrome Launch Configuration

    Next, from the debug panel you need to configure the launch script for chrome. If you don’t have any existing scripts, then you can just select one like “chrome” for example from the gear icon. It doesn’t really matter, as we are going to clear out the contents and replace it anyway.

    Let’s go to the official create-react-app documentation and grab the launch configuration to debug your web application. Just copy the whole snippet, and paste it in your launch.json file.

    Screenshot of Launch Configuration

    NOTE: The following snippet may change as create-react-app evolves. Please refer to the official documentation for the latest configuration snippet.

    { "version": "0.2.0", "configurations": [{ "name": "Chrome", "type": "chrome", "request": "launch", "url": "http://localhost:3000", "webRoot": "${workspaceRoot}/src", "sourceMapPathOverrides": { "webpack:///src/": "${webRoot}/" } }] 
  4. Launch Chrome Debugger

    And now, we are ready to debug our web app. Go up to the green arrow and make sure “Chrome” is selected in the dropdown, then click the green arrow.

    This will kick up yet another browser instance, one that is connected to VS Code’s debugger. At this point, you’ll probably need to refresh your browser to initiate your breakpoint.

    Soon we’ll reach our first breakpoint inside of VS Code!

    Screenshot of Live Debugger

    From here, you have access to look around at your local variables in the left panel. There are options to add watches, browse the call stack, etc… There is also a handy interactive Debug Console. For example, you can change the value of isFlipped to true to simulate that we actually clicked the joke.

    You can step over the breakpoint and hover over the classes variable to inspect it’s value at this point in time. For our bug, the problem is that the CardFlip-flipped className should have two dashes and not just one (as its using the SUIT CSS naming convention to indicate it’s a modifier). Thankfully, that’s easy to fix by adding an extra dash.

    Now, we can stop the debugger and retry our web app and sure enough, it works just fine!

    Screenshot of Live Debugger

Debugging Unit Tests

Now that we have our web application code all fixed up, let’s move to debugging our Jest unit tests.

  1. Debug CRA Tests Launch Configuration

    Here we have some code testing the behavior of our CardFlip React component.

    Screenshot of Failing Tests

    However, if we come to the terminal and run our Jest tests you’ll notice that one of them is failing at the moment. Let’s go inside and add a breakpoint to debug our code.

    Unfortunately, our previous launch script will not help us in this situation, but we can also go out to the official documentation to find the snippet we need. From the documentation you can copy the configuration section, add it to the array that you already have in your launch.json, and save the file.

    Screenshot of Debugging Tests

    NOTE: The following snippet may change as create-react-app evolves. Please refer to the official documentation for the latest configuration snippet.

    { "version": "0.2.0", "configurations": [ { "name": "Debug CRA Tests", "type": "node", "request": "launch", "runtimeExecutable": "${workspaceRoot}/node_modules/.bin/react-scripts", "args": [ "test", "--runInBand", "--no-cache", "--env=jsdom" ], "cwd": "${workspaceRoot}", "protocol": "inspector", "console": "integratedTerminal", "internalConsoleOptions": "neverOpen" } ] 
  2. Launch Debug CRA Tests Debugger

    Now, switch the option in the dropdown to “Debug CRA Test” and click the green arrow. This will kick off Jest and then VS Code will stop at our breakpoint.

    Screenshot of Debugging Tests

    Like before, we could look at the local variables panel, but we will come down to the debug console and inspect the DOM element’s text context. Ohhhh, hello has a 1 instead of an l in it. Let’s fix that, save, and rerun our tests. Yup, that was it. Our tests are all green now.

    Screenshot of Debugging Tests


Thanks for reading this second post in the create-react-app series. The above video is the first in a series, so stay tuned. You may also want to subscribe to the Manorisms YouTube Channel to make sure you are notified when new material is posted.

If you enjoyed this post, please consider sharing it with others via the following Twitter, Reddit, and/or Hacker News buttons. As always, you can reach out to me on Twitter at @elijahmanor. Thanks and have a blessed day!

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