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ChompChomp Development Guide

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Congratulations! So you want to get involved in ChompChomp’s development. Your contributions will be greatly appreciated.

Table of Contents


You’ll need the following already set up in order to follow the setup portion of this guide:


You can go the table of contents in order to jump to any section of setup.

Node.js Setup

  1. Navigate to the Node.js website and download the latest LTS installer. You are encouraged to download any additional tools reccommended by Node.js.

Note: if you are a Linux user, you may have to access a NodeSource distribution. It is assumed that if you are a Linux user you know what you are doing.

Expo Setup

  1. Open a Terminal and run

    npm i expo-cli --global
  2. Log in to expo with the command:

    expo login

    This will bring up a page in your web browser where you can either login or create an account on Expo’s servers. Join the Dudes of 708 development team (owner: Gideon Tong).

Device Setup

If you have an Android device, jump to the Android device setup section. If you have an iOS device, jump to the iOS device setup section. You can set up both if you have both.

Android Device Setup

  1. Download the Expo Go app from the Play Store.
  2. Log into your Expo account. Every step after this is optional.

Expo Go on the Play Store

Optional Steps:

  1. Download the Android SDK Platform Tools onto your computer.
  2. Extract the folder to a folder on your computer you won’t easily delete, like C:\Software\platform-tools on Windows or /home/<username>/platform-tools on macOS or Linux.
  3. Open a Terminal or Command Prompt window and navigate to the folder you extracted using the cd (change directory) command. For example, if I extracted it to C:\Software\platform-tools, I would write cd C:\Software\platform-tools.
  4. On your Android device, enable Developer Options. First navigate to Settings, and scroll to the bottom and find About Phone.
  5. Tap Build Number seven times. You should see a toast telling you Developer Mode is now enabled.
  6. Navigate back one screen, and you’ll find a Developer Options button. Tap it, and enable the option that says something like Enable USB debugging. The exact wording may depend on your device and version of Android.
  7. Plug your Android device into your computer. In your Terminal, type adb devices on Windows or ./adb devices for macOS and Linux computers.
  8. If prompted on your Android device, accept the prompt to allow USB debugging on your device.

iOS Device Setup

  1. Download the Expo Go app from the App Store.
  2. Log into your Expo account.

If you own a Mac, there are additional advanced setup steps you can take advantage of, but they will not be covered in this guide beacuse I don’t own a Mac. If you are a Mac user and would like to contribute usage of Xcode or other iOS debugging tools, by all means, please submit an improvement for this section.

Expo Go on the App Store


If you already have an editor you like, jump to project structure.


I personally use VS Code, but I’m going to try to cover all the potential ways you may want to develop. If you don’t already use an editor, download VS Code and head on to the VS Code section

Otherwise, pick your editor of choice:

VS Code

VS Code

You can download VS Code at this link. Thankfully, because VS Code is designed as an Electron app, it provides Javascript/Typescript extensions, debugging, and IntelliSense out of the box. ChompChomp is written in pure Javascript with React extensions, and does not support Typescript at this time.

This is really all you need, but you should set up Expo Tools and React Native Tools (both are one click extensions to add) for your VS Code environment.

Next, proceed to setting up.



Why are you reading this if you already know your way around Vim? Set it up for JavaScript/TypeScript bindings and you’ll be fine. Next, proceed to setting up.

Expo Snack

Expo Snack

This isn’t actually a screenshot of the code, but this is Expo Snack.

Expo Snack runs in the browser and basically acts like a Repl.it, if you have used that before. It provides a way to develop and test without leaving your browser. You can access it here.

It provides all the libraries and tools built-in, and is a conveneint way to develop. It isn’t officially supported by ChompChomp but you are free to use this to develop if you wish to sync your changes to git manually.

Next, proceed to setting up.


Xcode is the official code editor by Apple for Macs, and is only available for macOS. You can download it at this link. It is also the only way to self-compile the iOS version of ChompChomp, so you’ll need to follow this setup guide even if you don’t use Xcode normally so you can compile.

Download Xcode from the link above and run it. Apple will set up all the developer tools for you automatically. You’ll also need an Apple ID, which frankly is weird if you have a Mac but don’t have one.

Next, proceed to setting up.

Setting Up

  1. Clone the ChompChomp repository. If you don’t know how, please see the setting up git guide.
  2. Open Terminal or Command Prompt and navigate to the ChompChomp repository you cloned. Then run

    npm ci

    This process will take several minutes to complete if you’re running for the first time. If you need to update your packages, use the following command instead:

    npm i

Project Structure

If you are curious how the files are laid out, please see file structure, or you can see the code structure if you want to get a sense of how the code is formatted so you can make similar contributions.

File Structure

The project is broken up into a few important folders and files (you can click on the names of files and folders to view them):

Code Structure

A quick overview of the way our code is structured:

Components appear in the components folder and represent parts of views that may or may not be reused. This can include selection boxes, dialog boxes, repeated text input boxes, etc.

Views appear in the views folder, and there is one file/function for every view that appears in the app. Each one is linked to the App.js file.

Data Storage Format

The app stores a few pieces of information

Queue Data

Queue data is stored in the key queue and is stored as a JSON string array. Each element is a JSON object containing several keys:

An example is below:

    "type": "new",
    "payload": {
      "date": "2021-04-18T22:34:11.088180+00:00",
      "store": "7 West Los Angeles, CA",
      "name": "String Cheese",
      "price": "1.99",
      "weight": "16",
      "barcode": "01234567"
    "type": "update",
    "payload": {
      "barcode": "87654321",
      "store": "65 Danville, CA",
      "date": "2021-04-19T22:34:29.089034+00:00",
      "price": "2.99"
    "type": "quick",
    "payload": {
      "barcode": "55555555",
      "images": [
History Data

History data is stored in the key history and is stored as a JSON string array. Each element is a string containing the name of the item uploaded to the database. If there is more than the maximum in the list, the oldest is pushed off the list (it behaves as a queue).

An example is below:

  "String Cheese",
  "Cheddar Cheese",
  "Mozarella Cheese",
  "American Cheese",
  "Feta Cheese"

Making an Edit

Use an editor of your choice to edit a file, and the commit it. If you don’t know how, see the guide to using git.

Testing Your Changes

Run this command to start the development server:

expo start

Building the App

Your changes are automatically built whenever you change the version number in app.json. Simply bump the minor revision number by 1 and you’ll get a build back within the hour. Typically builds on the server take about 20-30 minutes for Android and 10-20 minutes for iOS. iOS builds are currently not supported by the ChompChomp development server, as you get a package back, so you’ll need to build iOS manually.

Step by step:

  1. Open the app.json file.
  2. Find the version number that says something like 1.0.0.
  3. Change the number so it says 1.0.1.
  4. Save and commit your changes.

To build for iOS and test it on your device as a fully compiled app, head below to iOS Builds. To build it for Android instead, head below to Android Builds.

iOS Builds

Warning: You can only build iOS builds on macOS.

Run the following command:

expo build:ios

This builds an IPA for distribution on Expo’s servers, which will take approximately 5-30 minutes. We do not currently have a macOS development server, and are looking to fundraise some money to host such a server.

You will be able to use this IPA provided you are either in the team (and have access to the development account), or you have your own development account.

Android Builds

Run the following command:

expo build:android -t apk

This builds an APK for distribution on Expo’s servers, which will take approximately 5-30 minutes. If you’d like to use the Dudes of 708 development server instead, please contact Gideon for the server information and additional setup instructions.

Deploying Updates

Upload the new build to the Dudes of 708 Google Drive in the format for iOS builds: ChompChomp-vX.X.X-archive.ipa or for Android builds: ChompChomp-vX.X.X-signed.apk. The build will be automatically deployed. Ensure you do not overwrite an existing file, because then the build will not be deployed.