Providing a Better Developer Experience with the Expo Snack App

We simplified Expo Snack, creating a setup-free, web-based editor with instant device preview. Now, it’s more accessible for beginners and efficient for experienced developers.

CLIENT INFO
Snack is one of the many Expo projects aimed at making working with React Native and Expo easier.
Industry
IT & Software
Company type
SME
Region
United States
tech INFO
We made it easier to experiment with React Native code in Snack.
Technologies
React Native | Expo
Platforms
Web-based editor
Tech Stack
Webpack | Ace Editor | custom ESLint
KEY RESULT
Before 14.5s
After 2.5s
35k
lines of code
7
months of work
800
code commits
88%
decreased shimmer render time
50%
quicker load times for chats on subsequent visits
50%
faster rendering time for chats
18%
less frame junk when scrolling
before
The refresh time was 5-11 seconds
after
The refresh time was reduced to ~2 s

Instant Preview

Developers can instantly preview code changes on real devices without a complex setup.
Expo Snack
CHALLENGE

Starting a React Native project involves setting up the developer environment and tools, ensuring stability with dependency management like yarn.lock or package-lock.json to prevent sudden failures.

We aimed to create a zero-setup solution for instant real device preview and easy sharing. We faced several challenges in the process:

  • Complex Setup: Traditional React Native development requires extensive setup.
  • Platform Knowledge: Developers need to understand both web and native tools.
  • Speed and Reliability: Running metro-bundler was slow and unreliable.
SOLUTIONS IMPLEMENTED

MINIMIZED SETUP

Leveraged Expo's development environment to reduce initial setup time.

WEB-BASED EDITOR

Used Ace Editor with custom ESLint for a smooth coding experience.

CUSTOM PACKAGER

Created bundles with Webpack, allowing easy module imports.

INSTANT PREVIEW

Enabled code preview on real devices via the Expo app by patching code changes dynamically.

To avoid running metro-bundler, we opted to patch code changes instead of rebuilding the entire bundle. We chose Ace Editor for the web-based editor, incorporating a custom ESLint build for linting.

define
Identified confirmed/reported issues such as re-renders and created a backlog for potential improvements.
measure
Used Macro tool measurements.
ANALYZE
Selected the most promising performance changes.
IMPROVE
Implemented changes following React Native best practices.
CONTROL
Re-measured with the Marco tool and compared to the 4.58.0 native version.
Deployment
 Developed the release process for both Android and iOS.
API DESIGN
Proposed an API based on the Rive Android library features.
INTEGRATION
Implemented Rive SDK integration for Android and created an example app for testing.
iOS SUPPORT
Extended the integration to iOS after successful Android testing.
AUTOMATION
Created a Github Action workflow for automated library releases.
PUBLIC RELEASE
Made the library publicly available on platforms like CocoaPods and Maven.
DEPENDENCIES
Managing dependencies, including Expo and react-native packages for each new release.
RELEASES
Automating the release process with custom GitHub Actions.
TRAINING
Providing React Native training through pair programming, code reviews, and workshops.
USE CASES

BETTER DEVELOPER EXPERIENCE

By enhancing Snack, we aimed to cater to various groups and their use cases:
01
CODE REFACTORING
Kicked off the project with refactoring the whole socket.MIGRATION Migrated the codebase to TypeScript.
02
MIGRATION
Migrated the codebase to TypeScript.
03
DEPENDENCIES
Upgraded major dependencies such as Expo, React Navigation, and React Query.
04
PAYMENTS
Created two options: In-app purchase with Google Play or App Store and credit card payment.
05
linking
Sorted out links, integrated content, and implemented html rendering.
We provided full front-end support, project configuration, feature parity, and expert advice on technical and user experience. We also implemented a new design guideline, including dark mode with auto theme detection.
01
RN PAPER
Forked the React Native Paper library.
02
ci
Established continuous integration for automated code updates.
03
testing
Set up a Storybook for component testing.
04
design
Developed the basis of the design – color, layout, and typography.
Once we had the basics down, we started working on the UI library components. The components we developed included: AppBar, TextField. Button, Icon Button, Toast, which included animation and swipe-to-dismiss, Match Status, Search, and many more!
Apart from all the fixes and improvements, we provided metrics that should be tracked over time so the client knows exactly what to monitor and correct to maintain great performance levels long term.
16.8s
App start time, before 48.5s
 8.6s
Report screen load time, before 15.9s
2.5s
Sending a message, before 14.5s
60FPS
Average FPS on LHN
2.6s
Search screen load time, before 11.8s
01
Together
we acted as staff augmentation within Advantys’ team.
02
Engaged
in collaborative problem-solving and solution exploration.
03
supervised
by Advantys' CTO, the project utilized GitHub, Notion, and Slack for communication.
01
migrating
from a custom server-side rendering (SSR) solution to Next.js 
02
Focusing
on Core Web Vitals metrics
03
Optimizing
a large shared JS bundle 
04
Introducing
Fast Refresh for accelerated development iterations
The introduction of Fast Refresh in Next.js further accelerated development iterations. All in all, it contributed to an enhanced user and developer experience.In a span of several months, our team effectively overhauled the AutoZone app's performance, which initially struggled on both desktop and mobile devices. To find out more about the whole AutoZone project, head over to the case study on main case study title
01
strong
architecture with professional maintenance and continuous updates
02
high
code coverage with quality-compliant unit and integration tests
03
Comprehensive
testing, including end-to-end.
04
Faster
time-to-market with mobile process automation.
05
New PoC
features like biometrics and mobile health kit integration.
Last but not least, our collaboration significantly enhanced the knowledge of Thriva's development team regarding React and React Native.
Autozone app
  • Enhanced app performance by over 200%.
  • Improved Core Web Vitals metrics to meet Google's standards.
  • Reduced refresh time to ~2s with Fast Refresh feature.
  • Improve code quality and ongoing efforts to add advanced functionalities
  • Students new to programming and React Native
  • Web developers unfamiliar with device APIs and native apps
  • Native developers exploring web app frameworks and React Native's UX potential
  • React Native developers prototyping and sharing ideas
  • Library maintainers creating examples and documentation
  • Users providing reproducible cases for bug reports
  • Speakers and workshop presenters conducting live coding sessions
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RESULTS

We successfully met our initial goals and continue to enhance the experience with ongoing iterations and feature additions.

Key features include:

  • A user-friendly web-based editor for rapid deployment without setup
  • Instant preview on real devices via the Expo app
  • Effective debugging with console logs
  • Seamless sharing through easily accessible links
  • Embeddable editor for documentation

Our commitment to reducing barriers and fostering experimentation with Snack is our contribution to the community, and we look forward to seeing the innovative ideas it sparks.

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Providing a Better Developer Experience with the Expo Snack App

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Not only does Callstack have tremendously talented engineers, but I know they care about the success of the project as much as I do. Having a true partner is a wonderful experience and gives us the ability to move so much faster than we could without them.

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Product Expo

In brief

We optimized the client’s mobile app performance and introduced a custom tool to measure performance regressions. We set up performance tests and documentation to enable a seamless transition of knowledge with the in-house team of developers.

Client Info
Entain is one of the world’s largest sports betting and gaming entertainment groups.
Industry
Commercial gaming
Company type
Enterprise
Region
Australia, Asia & Oceania
Tech Info
Performance optimization project with the best practices, approaches & tech solutions
Technologies
React Native | Native
Platforms
iOS | Android
Stack
Redux | Tanstack | Reassure | GraphQL

Performance Boost

87.5%

In 87.5% of the screens, the number of rerenders decreased or remained the same, which affected the acceleration of the initial performance.

React Universe

In brief

Snack is the easiest way to experiment and explore working React Native code. It is the first stop for anyone curious what RN is all about, and a constant companion for experienced developers to experiment, collaborate and learn.

The easiest way to experiment and explore working with React Native code

With Snack, it’s possible to prototype a React Native app on its web based editor and instantly preview it on the device with the Expo app or the web based simulator.
Snack is one of the many projects from Expo, aimed to make working with React Native and Expo easier.

Expo Snack App screenshot

This poses a great barrier to people who want to try out React Native.

With Snack, we wanted to make this easier by addressing following groups of people and their use cases:

Starting a React Native project is a lot of work, including setting up the developer environment and various tools. In addition, projects which were working few days earlier could stop working without any changes if not using something like a yarn.lock or package-lock.json.

  • Students with limited to no background knowledge with programming and/or ReactNative,
  • Web developers unfamiliar with device APIs and building native apps,
  • Native developers unfamiliar with Web app development frameworks and willing to experiment if it’s possible to provide good user experience with React Native,
  • ReactNative developers wanting to prototype and share an idea,
  • Library maintainers wanting to provide examples and documentations,
  • Users trying to provide a repro case when reporting a bug
  • Speakers and workshop presenters wanting to do a live coding session

We needed to build something that requires no setup, can be previewed instantly on real devices and easily shared with others. We faced several challenges:

  • React Native spans multiple languages; to be able to setup the developer environment, the developer doesn’t only have to be familiar with Web app development tools, but also native development tools such as Android Studio and XCode
  • Running React Native’s packager, i.e. metro-bundler was a solution, but it was really slow and unreliable
  • Being able to try the code out on a web based simulator was a nice convenience (as on rnplay.org), but we needed to be able to test on a real device to be actually able to try the real thing
  • Ability to install modules from NPM was necessary for a lot of scenarios

We also needed to build a web based editor which provides a good editing experience with linting, managing multiple files with drag and drop, logging etc.

Minimize the setup

The first problem we needed to solve was to minimize the setup required. Fortunately, the expo development environment already takes care of this. While using Expo would solve this issue, it still took a little bit of work. Another approach was to run a React Native development environment on the cloud (rnplay.org) RNPlay. However it was really slow and unusable. To avoid running metro-bundler, we decided to patch in the code that has changed instead of rebuilding the full bundle every time. For the web based editor, we decided to use Ace Editor with a custom ESLint build for linting the files.

Web based editor with a companion app

Our final approach involved a web based editor with a companion app running inside the Expo app on the device which patches in the changed code. The Expo app can load the experience by opening a link to the snack or by scanning a QR code.

The basic approach is that the web UI sends the code and the list of dependencies to the app, the app downloads the dependencies, transforms the code with Babel, and then executes it. Source

Expo Snack App screenshot

We used Ace Editor for the code editor with various enhancements to improve the editing experience, such as ESLint and Prettier integration, various keyboard shortcut, file management support etc.: source

Expo Snack App screenshot

We also built a custom packager which creates bundles to be used by projects on Snack, so you could import a module like usual and we take care of the rest behind the scenes. The packager is based on webpack with custom loaders and plugins: sourcePreview results instantly on a real device using the Expo app

Expo Snack App screenshot

Preview results instantly on a real device using the Expo app

We managed to achieve the goals we originally set and constantly iterating on improving the experience and adding new features.

  • Easy to use web based editor which lets the developer start quickly without setting up a developer environment,
  • Preview results instantly on real device using the expo app
  • Debugging capabilities with console logs
  • Easily shareable links
  • Embeddable editor for documentation


We’re happy to be able to help the community by lowering the barriers to entry and experimentation with Snack and excited to see what new ideas the community comes up with. If you are using React Native and haven’t checked it out yet, you definitely should!

The challenges we’ve solved so far

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