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This guide walks you through cloning an example JavaScript application that uses [Puppeteer](🔗) for browser automation, making some changes, and seeing the visual differences in Percy's visual review tool. The example application is a to-do app, forked from [todomvc](🔗).

The tutorial assumes you're already familiar with JavaScript and [Puppeteer](🔗) and focuses on using it with Percy. You'll still be able to follow along if you're not familiar with Puppeteer, but we won't spend time introducing Puppeteer concepts.

The tutorial also assumes you have [node with npm](🔗) and [git](🔗) installed.

**Step 1:** Clone the example application and install dependencies:

The example app will now be ready to go. You can explore the app by opening the [`index.html`](🔗) file in a browser.

**Step 2:** Sign in to Percy, create a new organization, and create a new project. You can name both the organization and project 'todo'.

After you've created the project, you'll be shown a token environment variable.

**Step 3:** In the shell window you're working in, export the token environment variable:

Note: usually this would only be set up in your [CI environment](🔗), but to keep things simple we'll configure it in your shell so that Percy is enabled in your local environment.

**Step 4:** Check out a new branch for your work in this tutorial (we'll call this branch `tutorial-example`), and run the Puppeteer script to take snapshots:

This will run [`puppeteer_snapshots.js`](🔗), which contains calls to create and upload Percy snapshots. The snapshots will then be uploaded to Percy for comparison. Percy will use the token you used in Step 2 to know which organization and project to upload the snapshots to.

You can view the screenshots in Percy now if you want, but there will be no visual comparisons yet. You'll see that Percy shows you that these snapshots come from your `tutorial-example` branch.


**Step 5:** Use your text editor to edit `index.html` and introduce some visual change. For example, you can add a `<strong>` tag to the "Active" button on line 25. After the change, that line looks like this:

**Step 7:** Commit the change:

**Step 8:** Run the snapshots again:

This will take new snapshots of our modified application. The new snapshots will be uploaded to Percy and compared with the previous snapshots, showing any visual diffs.

At the end of the run output, you will see logs from Percy confirming that the snapshots were successfully uploaded, and giving you a direct URL to check out any visual diffs.

**Step 9:** Visit your project in Percy and you'll see a new build with the visual comparisons between the two runs. Click anywhere on the Build 2 row. You can see the original snapshots on the left, and the new snapshots on the right.

Percy has highlighted what's changed visually in the app! Snapshots with the largest changes are shown first You can click on the highlight to reveal the underlying screenshot.


If you scroll down, you'll see that no other snapshots were affected by our changes to the 'Clear completed' button. The unchanged snapshots appear grouped together at the bottom of the list.

**Finished!** 😀

From here, you can try making your own changes to the app, if you like. If you do, re-run the snapshots script, and then you'll see any visual changes reflected in Percy.

This tutorial used an app with Puppeteer and Percy already added. You can see how we [added Percy and Puppeteer to our app](🔗), or check out the [docs](🔗) to learn how to add Percy to your own Puppeteer scripts.