This guide is for people stuck on how to get started. For details after this guide, refer to the official Expo documentation for the specific feature you are working on.
This guide explains how to set up and run the Expo mobile app on your physical Android or iOS device using Expo Go.
Clone the Repository Clone the project repository to your local machine:
git clone <repository-url>
Navigate to the Mobile Directory Change to the mobile directory:
cd mobile
Install Dependencies
Do not use npm install. Instead, as specified in the main README, run the following command to install the required node_modules (only needed the first time):
yarn install
Set Up Your Environment Follow the Expo environment setup guide for your platform:
Download Expo Go Install the Expo Go app on your device:
Start the App
Do not use npx expo start. Instead, as specified in the main README, run the following command to start the Expo development server:
yarn expo start
Scan the QR code displayed in the terminal with the Expo Go app on your device.
Troubleshooting If the QR code scan fails, try starting the app with a tunnel:
yarn expo start --tunnel
Then scan the new QR code.
Hey team! Since we can’t afford GitHub Teams or use branch protection rules, we need to take responsibility and follow this workflow to keep our project organized and safe. Let’s do this right and make an awesome app! 🎉
To ensure consistency and speed, we use Yarn exclusively. Please avoid using npm or pnpm commands.
| Task | npm command | Yarn command |
|---|---|---|
| Install dependencies | npm install or npm i |
yarn install or yarn |
| Add a package | npm install <pkg> |
yarn add <pkg> |
| Add a dev dependency | npm install <pkg> --save-dev |
yarn add <pkg> --dev |
| Remove a package | npm uninstall <pkg> |
yarn remove <pkg> |
| Upgrade a package | npm update <pkg> |
yarn upgrade <pkg> |
| Run a script | npm run <script> |
yarn <script> |
| Run one-off command | npx <cmd> |
yarn dlx <cmd> |
| List installed packages | npm list |
yarn list |
| Check outdated packages | npm outdated |
yarn outdated |
| Clean cache | npm cache clean --force |
yarn cache clean |
| Generate lockfile only | npm install --package-lock-only |
yarn install --mode=update-lockfile |
| Rebuild node_modules | npm rebuild |
yarn rebuild |
| Run tests | npm test |
yarn test |
These conversions work for most cases but always double-check if any edge cases arise.
npm install or pnpm install to manage dependencies; our scripts will block those commands.yarn.lock to keep dependency versions consistent across all machines.We’ll use three types of branches to keep things clear:
stable
Our production-ready branch. Only fully tested, working code goes here—think of it as the app version we’d show the world.
main
Our development branch. This is where we combine reviewed changes before they’re ready for stable.
Feature Branches
Your personal workspace! Each of us creates a branch for our tasks (e.g., feature-login, fix-bug).
Here’s our step-by-step process:
Start Fresh
Create your feature branch from the latest main. Name it something clear like feature-login.
Do Your Thing
Work on your task and save your changes with short, descriptive messages.
Share Your Work
Push your branch to GitHub.
Request a Review
Open a Pull Request (PR) from your branch to main. Ask at least one teammate to review it.
Merge with Care
After approval, the reviewer merges your PR into main. NEVER push directly to main or stable!
Prep for Production
Once main is tested and solid, we’ll merge it into stable together.
main or stable.main before starting or pushing new work.feature-login-form, fix-null-crash, refactor-user-service.main safe. Only push clean, functional code ready for review.💡 Example: If you add a
calculateTotal()function, write tests for expected and edge case inputs.
main.Since we’re on GitHub’s free tier, we don’t have fancy protections. This workflow:
stable is always ready to shine.main or stable could CRASH THE APP for everyone!We’re the only ones keeping this safe—let’s stick to it!
✨ We're all still learning!
Don’t feel overwhelmed by this guide—it’s here to help us work better together. Even the best devs get stuck, so don’t hesitate to ask the team for help at any point. Collaboration beats confusion.
A mostly reasonable approach to React and JSX
This style guide is mostly based on the standards that are currently prevalent in JavaScript, although some conventions (i.e async/await or static class fields) may still be included or prohibited on a case-by-case basis. Currently, anything prior to stage 3 is not included nor recommended in this guide.
React.createClass vs statelessisMountedreact/no-multi-comp.React.createElement unless you’re initializing the app from a file that is not JSX.react/forbid-prop-types will allow arrays and objects only if it is explicitly noted what array and object contains, using arrayOf, objectOf, or shape.React.createClass vs statelessIf you have internal state and/or refs, prefer class extends React.Component over React.createClass. eslint: react/prefer-es6-class react/prefer-stateless-function
// bad
const Listing = React.createClass({
// ...
render() {
return <div>{this.state.hello}</div>;
},
});
// good
class Listing extends React.Component {
// ...
render() {
return <div>{this.state.hello}</div>;
}
}
And if you don’t have state or refs, prefer normal functions (not arrow functions) over classes:
// bad
class Listing extends React.Component {
render() {
return <div>{this.props.hello}</div>;
}
}
// bad (relying on function name inference is discouraged)
const Listing = ({ hello }) => <div>{hello}</div>;
// good
function Listing({ hello }) {
return <div>{hello}</div>;
}
Why? Mixins introduce implicit dependencies, cause name clashes, and cause snowballing complexity. Most use cases for mixins can be accomplished in better ways via components, higher-order components, or utility modules.
Extensions: Use .jsx extension for React components. eslint: react/jsx-filename-extension
Filename: Use PascalCase for filenames. E.g., ReservationCard.jsx.
Reference Naming: Use PascalCase for React components and camelCase for their instances. eslint: react/jsx-pascal-case
// bad
import reservationCard from './ReservationCard';
// good
import ReservationCard from './ReservationCard';
// bad
const ReservationItem = <ReservationCard />;
// good
const reservationItem = <ReservationCard />;
Component Naming: Use the filename as the component name. For example, ReservationCard.jsx should have a reference name of ReservationCard. However, for root components of a directory, use index.jsx as the filename and use the directory name as the component name:
// bad
import Footer from './Footer/Footer';
// bad
import Footer from './Footer/index';
// good
import Footer from './Footer';
Higher-order Component Naming: Use a composite of the higher-order component’s name and the passed-in component’s name as the displayName on the generated component. For example, the higher-order component withFoo(), when passed a component Bar should produce a component with a displayName of withFoo(Bar).
Why? A component’s
displayNamemay be used by developer tools or in error messages, and having a value that clearly expresses this relationship helps people understand what is happening.
// bad
export default function withFoo(WrappedComponent) {
return function WithFoo(props) {
return <WrappedComponent {...props} foo />;
};
}
// good
export default function withFoo(WrappedComponent) {
function WithFoo(props) {
return <WrappedComponent {...props} foo />;
}
const wrappedComponentName =
WrappedComponent.displayName || WrappedComponent.name || 'Component';
WithFoo.displayName = `withFoo(${wrappedComponentName})`;
return WithFoo;
}
Props Naming: Avoid using DOM component prop names for different purposes.
Why? People expect props like
styleandclassNameto mean one specific thing. Varying this API for a subset of your app makes the code less readable and less maintainable, and may cause bugs.
// bad
<MyComponent style="fancy" />
// bad
<MyComponent className="fancy" />
// good
<MyComponent variant="fancy" />
Do not use displayName for naming components. Instead, name the component by reference.
// bad
export default React.createClass({
displayName: 'ReservationCard',
// stuff goes here
});
// good
export default class ReservationCard extends React.Component {}
Follow these alignment styles for JSX syntax. eslint: react/jsx-closing-bracket-location react/jsx-closing-tag-location
// bad
<Foo superLongParam="bar"
anotherSuperLongParam="baz" />
// good
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
/>
// if props fit in one line then keep it on the same line
<Foo bar="bar" />
// children get indented normally
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
>
<Quux />
</Foo>
// bad
{showButton &&
<Button />
}
// bad
{
showButton &&
<Button />
}
// good
{showButton && (
<Button />
)}
// good
{showButton && <Button />}
// good
{someReallyLongConditional
&& anotherLongConditional
&& (
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
/>
)
}
// good
{someConditional ? (
<Foo />
) : (
<Foo
superLongParam="bar"
anotherSuperLongParam="baz"
/>
)}
Always use double quotes (") for JSX attributes, but single quotes (') for all other JS. eslint: jsx-quotes
Why? Regular HTML attributes also typically use double quotes instead of single, so JSX attributes mirror this convention.
// bad
<Foo bar='bar' />
// good
<Foo bar="bar" />
// bad
<Foo style={{ left: "20px" }} />
// good
<Foo style={{ left: '20px' }} />
Always include a single space in your self-closing tag. eslint: no-multi-spaces, react/jsx-tag-spacing
// bad
<Foo/>
// very bad
<Foo />
// bad
<Foo
/>
// good
<Foo />
Do not pad JSX curly braces with spaces. eslint: react/jsx-curly-spacing
// bad
<Foo bar={ baz } />
// good
<Foo bar={baz} />
Always use camelCase for prop names, or PascalCase if the prop value is a React component.
// bad
<Foo
UserName="hello"
phone_number={12345678}
/>
// good
<Foo
userName="hello"
phoneNumber={12345678}
Component={SomeComponent}
/>
Omit the value of the prop when it is explicitly true. eslint: react/jsx-boolean-value
// bad
<Foo
hidden={true}
/>
// good
<Foo
hidden
/>
// good
<Foo hidden />
Always include an alt prop on <img> tags. If the image is presentational, alt can be an empty string or the <img> must have role="presentation". eslint: jsx-a11y/alt-text
// bad
<img src="hello.jpg" />
// good
<img src="hello.jpg" alt="Me waving hello" />
// good
<img src="hello.jpg" alt="" />
// good
<img src="hello.jpg" role="presentation" />
Do not use words like "image", "photo", or "picture" in <img> alt props. eslint: jsx-a11y/img-redundant-alt
Why? Screenreaders already announce
imgelements as images, so there is no need to include this information in the alt text.
// bad
<img src="hello.jpg" alt="Picture of me waving hello" />
// good
<img src="hello.jpg" alt="Me waving hello" />
Use only valid, non-abstract ARIA roles. eslint: jsx-a11y/aria-role
// bad - not an ARIA role
<div role="datepicker" />
// bad - abstract ARIA role
<div role="range" />
// good
<div role="button" />
Do not use accessKey on elements. eslint: jsx-a11y/no-access-key
Why? Inconsistencies between keyboard shortcuts and keyboard commands used by people using screenreaders and keyboards complicate accessibility.
// bad
<div accessKey="h" />
// good
<div />
key prop, prefer a stable ID. eslint: react/no-array-index-keyWhy? Not using a stable ID is an anti-pattern because it can negatively impact performance and cause issues with component state.
We don’t recommend using indexes for keys if the order of items may change.
// bad
{
todos.map((todo, index) => <Todo {...todo} key={index} />);
}
// good
{
todos.map(todo => <Todo {...todo} key={todo.id} />);
}
Why? propTypes are a form of documentation, and providing defaultProps means the reader of your code doesn’t have to assume as much. In addition, it can mean that your code can omit certain type checks.
// bad
function SFC({ foo, bar, children }) {
return (
<div>
{foo}
{bar}
{children}
</div>
);
}
SFC.propTypes = {
foo: PropTypes.number.isRequired,
bar: PropTypes.string,
children: PropTypes.node,
};
// good
function SFC({ foo, bar, children }) {
return (
<div>
{foo}
{bar}
{children}
</div>
);
}
SFC.propTypes = {
foo: PropTypes.number.isRequired,
bar: PropTypes.string,
children: PropTypes.node,
};
SFC.defaultProps = {
bar: '',
children: null,
};
Why? Otherwise you’re more likely to pass unnecessary props down to components. And for React v15.6.1 and older, you could pass invalid HTML attributes to the DOM.
Exceptions:
function HOC(WrappedComponent) {
return class Proxy extends React.Component {
Proxy.propTypes = {
text: PropTypes.string,
isLoading: PropTypes.bool
};
render() {
return <WrappedComponent {...this.props} />
}
}
}
export default function Foo {
const props = {
text: '',
isPublished: false
}
return (<div {...props} />);
}
Notes for use: Filter out unnecessary props when possible. Also, use prop-types-exact to help prevent bugs.
// bad
render() {
const { irrelevantProp, ...relevantProps } = this.props;
return <WrappedComponent {...this.props} />
}
// good
render() {
const { irrelevantProp, ...relevantProps } = this.props;
return <WrappedComponent {...relevantProps} />
}
Always use ref callbacks. eslint: react/no-string-refs
// bad
<Foo
ref="myRef"
/>
// good
<Foo
ref={(ref) => { this.myRef = ref; }}
/>
Wrap JSX tags in parentheses when they span more than one line. eslint: react/jsx-wrap-multilines
// bad
render() {
return <MyComponent variant="long body" foo="bar">
<MyChild />
</MyComponent>;
}
// good
render() {
return (
<MyComponent variant="long body" foo="bar">
<MyChild />
</MyComponent>
);
}
// good, when single line
render() {
const body = <div>hello</div>;
return <MyComponent>{body}</MyComponent>;
}
Always self-close tags that have no children. eslint: react/self-closing-comp
// bad
<Foo variant="stuff"></Foo>
// good
<Foo variant="stuff" />
If your component has multiline properties, close its tag on a new line. eslint: react/jsx-closing-bracket-location
// bad
<Foo
bar="bar"
baz="baz" />
// good
<Foo
bar="bar"
baz="baz"
/>
Use arrow functions to close over local variables. It is handy when you need to pass additional data to an event handler. Although, make sure they do not massively hurt performance, in particular when passed to custom components that might be PureComponents, because they will trigger a possibly needless rerender every time.
function ItemList(props) {
return (
<ul>
{props.items.map((item, index) => (
<Item
key={item.key}
onClick={event => {
doSomethingWith(event, item.name, index);
}}
/>
))}
</ul>
);
}
Bind event handlers for the render method in the constructor. eslint: react/jsx-no-bind
Why? A bind call in the render path creates a brand new function on every single render. Do not use arrow functions in class fields, because it makes them challenging to test and debug, and can negatively impact performance, and because conceptually, class fields are for data, not logic.
// bad
class extends React.Component {
onClickDiv() {
// do stuff
}
render() {
return <div onClick={this.onClickDiv.bind(this)} />;
}
}
// very bad
class extends React.Component {
onClickDiv = () => {
// do stuff
}
render() {
return <div onClick={this.onClickDiv} />
}
}
// good
class extends React.Component {
constructor(props) {
super(props);
this.onClickDiv = this.onClickDiv.bind(this);
}
onClickDiv() {
// do stuff
}
render() {
return <div onClick={this.onClickDiv} />;
}
}
Do not use underscore prefix for internal methods of a React component.
Why? Underscore prefixes are sometimes used as a convention in other languages to denote privacy. But, unlike those languages, there is no native support for privacy in JavaScript, everything is public. Regardless of your intentions, adding underscore prefixes to your properties does not actually make them private, and any property (underscore-prefixed or not) should be treated as being public. See issues #1024, and #490 for a more in-depth discussion.
// bad
React.createClass({
_onClickSubmit() {
// do stuff
},
// other stuff
});
// good
class extends React.Component {
onClickSubmit() {
// do stuff
}
// other stuff
}
Be sure to return a value in your render methods. eslint: react/require-render-return
// bad
render() {
(<div />);
}
// good
render() {
return (<div />);
}
class extends React.Component:static methodsconstructorgetChildContextcomponentWillMountcomponentDidMountcomponentWillReceivePropsshouldComponentUpdatecomponentWillUpdatecomponentDidUpdatecomponentWillUnmounthandleSubmit() or handleChangeDescription()onClickSubmit() or onChangeDescription()render like getSelectReason() or getFooterContent()renderNavigation() or renderProfilePicture()renderHow to define propTypes, defaultProps, contextTypes, etc...
import React from 'react';
import PropTypes from 'prop-types';
const propTypes = {
id: PropTypes.number.isRequired,
url: PropTypes.string.isRequired,
text: PropTypes.string,
};
const defaultProps = {
text: 'Hello World',
};
class Link extends React.Component {
static methodsAreOk() {
return true;
}
render() {
return (
<a href={this.props.url} data-id={this.props.id}>
{this.props.text}
</a>
);
}
}
Link.propTypes = propTypes;
Link.defaultProps = defaultProps;
export default Link;
Ordering for React.createClass: eslint: react/sort-comp
displayNamepropTypescontextTypeschildContextTypesmixinsstaticsdefaultPropsgetDefaultPropsgetInitialStategetChildContextcomponentWillMountcomponentDidMountcomponentWillReceivePropsshouldComponentUpdatecomponentWillUpdatecomponentDidUpdatecomponentWillUnmountonClickSubmit() or onChangeDescription()render like getSelectReason() or getFooterContent()renderNavigation() or renderProfilePicture()renderisMountedisMounted. eslint: react/no-is-mountedWhy?
isMountedis an anti-pattern, is not available when using ES6 classes, and is on its way to being officially deprecated.