tweetping/wheel-ui repository overview

This project was bootstrapped with Create React App⁠.

Below you will find some information on how to perform common tasks.
You can find the most recent version of this guide here⁠.

⁠Table of Contents

• Updating to New Releases⁠
• Sending Feedback⁠
• Folder Structure⁠
• Available Scripts⁠
  • npm start⁠
  • npm test⁠
  • npm run build⁠
  • npm run eject⁠
• Displaying Lint Output in the Editor⁠
• Installing a Dependency⁠
• Importing a Component⁠
• Adding a Stylesheet⁠
• Post-Processing CSS⁠
• Adding Images and Fonts⁠
• Using the public Folder⁠
• Adding Bootstrap⁠
• Adding Flow⁠
• Adding Custom Environment Variables⁠
• Can I Use Decorators?⁠
• Integrating with a Node Backend⁠
• Proxying API Requests in Development⁠
• Using HTTPS in Development⁠
• Generating Dynamic <meta> Tags on the Server⁠
• Running Tests⁠
  • Filename Conventions⁠
  • Command Line Interface⁠
  • Version Control Integration⁠
  • Writing Tests⁠
  • Testing Components⁠
  • Using Third Party Assertion Libraries⁠
  • Initializing Test Environment⁠
  • Focusing and Excluding Tests⁠
  • Coverage Reporting⁠
  • Continuous Integration⁠
  • Disabling jsdom⁠
  • Experimental Snapshot Testing⁠
• Deployment⁠
  • Building for Relative Paths⁠
  • GitHub Pages⁠
  • Heroku⁠
  • Modulus⁠
  • Netlify⁠
  • Now⁠
  • Surge⁠
• Something Missing?⁠

⁠Updating to New Releases

Create React App is divided into two packages:

• create-react-app is a global command-line utility that you use to create new projects.
• react-scripts is a development dependency in the generated projects (including this one).

You almost never need to update create-react-app itself: it delegates all the setup to react-scripts.

When you run create-react-app, it always creates the project with the latest version of react-scripts so you’ll get all the new features and improvements in newly created apps automatically.

To update an existing project to a new version of react-scripts, open the changelog⁠, find the version you’re currently on (check package.json in this folder if you’re not sure), and apply the migration instructions for the newer versions.

In most cases bumping the react-scripts version in package.json and running npm install in this folder should be enough, but it’s good to consult the changelog⁠ for potential breaking changes.

We commit to keeping the breaking changes minimal so you can upgrade react-scripts painlessly.

⁠Sending Feedback

We are always open to your feedback⁠.

⁠Folder Structure

After creation, your project should look like this:

my-app/
  README.md
  node_modules/
  package.json
  public/
    index.html
    favicon.ico
  src/
    App.css
    App.js
    App.test.js
    index.css
    index.js
    logo.svg

For the project to build, these files must exist with exact filenames:

• public/index.html is the page template;
• src/index.js is the JavaScript entry point.

You can delete or rename the other files.

You may create subdirectories inside src. For faster rebuilds, only files inside src are processed by Webpack.
You need to put any JS and CSS files inside src, or Webpack won’t see them.

Only files inside public can be used from public/index.html.
Read instructions below for using assets from JavaScript and HTML.

You can, however, create more top-level directories.
They will not be included in the production build so you can use them for things like documentation.

⁠Available Scripts

In the project directory, you can run:

⁠npm start

Runs the app in the development mode.
Open http://localhost:3000⁠ to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

⁠npm test

Launches the test runner in the interactive watch mode.
See the section about running tests⁠ for more information.

⁠npm run build

Builds the app for production to the build folder.
It correctly bundles React in production mode and optimizes the build for the best performance.

The build is minified and the filenames include the hashes.
Your app is ready to be deployed!

⁠npm run eject

Note: this is a one-way operation. Once you eject, you can’t go back!

If you aren’t satisfied with the build tool and configuration choices, you can eject at any time. This command will remove the single build dependency from your project.

Instead, it will copy all the configuration files and the transitive dependencies (Webpack, Babel, ESLint, etc) right into your project so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point you’re on your own.

You don’t have to ever use eject. The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.

⁠Displaying Lint Output in the Editor

Some editors, including Sublime Text, Atom, and Visual Studio Code, provide plugins for ESLint.

They are not required for linting. You should see the linter output right in your terminal as well as the browser console. However, if you prefer the lint results to appear right in your editor, there are some extra steps you can do.

You would need to install an ESLint plugin for your editor first.

Then add this block to the package.json file of your project:

{
  // ...
  "eslintConfig": {
    "extends": "react-app"
  }
}

Finally, you will need to install some packages globally:

npm install -g [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected]

We recognize that this is suboptimal, but it is currently required due to the way we hide the ESLint dependency. The ESLint team is already working on a solution to this⁠ so this may become unnecessary in a couple of months.

⁠Installing a Dependency

The generated project includes React and ReactDOM as dependencies. It also includes a set of scripts used by Create React App as a development dependency. You may install other dependencies (for example, React Router) with npm:

npm install --save <library-name>

⁠Importing a Component

This project setup supports ES6 modules thanks to Babel.
While you can still use require() and module.exports, we encourage you to use import and export⁠ instead.

For example:

⁠Button.js

import React, { Component } from 'react';

class Button extends Component {
  render() {
    // ...
  }
}

export default Button; // Don’t forget to use export default!

⁠DangerButton.js

import React, { Component } from 'react';
import Button from './Button'; // Import a component from another file

class DangerButton extends Component {
  render() {
    return <Button color="red" />;
  }
}

export default DangerButton;

Be aware of the difference between default and named exports⁠. It is a common source of mistakes.

We suggest that you stick to using default imports and exports when a module only exports a single thing (for example, a component). That’s what you get when you use export default Button and import Button from './Button'.

Named exports are useful for utility modules that export several functions. A module may have at most one default export and as many named exports as you like.

Learn more about ES6 modules:

• When to use the curly braces?⁠
• Exploring ES6: Modules⁠
• Understanding ES6: Modules⁠

⁠Adding a Stylesheet

This project setup uses Webpack⁠ for handling all assets. Webpack offers a custom way of “extending” the concept of import beyond JavaScript. To express that a JavaScript file depends on a CSS file, you need to import the CSS from the JavaScript file:

⁠Button.css

.Button {
  padding: 20px;
}

⁠Button.js

import React, { Component } from 'react';
import './Button.css'; // Tell Webpack that Button.js uses these styles

class Button extends Component {
  render() {
    // You can use them as regular CSS styles
    return <div className="Button" />;
  }
}

This is not required for React but many people find this feature convenient. You can read about the benefits of this approach here⁠. However you should be aware that this makes your code less portable to other build tools and environments than Webpack.

In development, expressing dependencies this way allows your styles to be reloaded on the fly as you edit them. In production, all CSS files will be concatenated into a single minified .css file in the build output.

If you are concerned about using Webpack-specific semantics, you can put all your CSS right into src/index.css. It would still be imported from src/index.js, but you could always remove that import if you later migrate to a different build tool.

⁠Post-Processing CSS

This project setup minifies your CSS and adds vendor prefixes to it automatically through Autoprefixer⁠ so you don’t need to worry about it.

For example, this:

.App {
  display: flex;
  flex-direction: row;
  align-items: center;
}

becomes this:

.App {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: horizontal;
  -webkit-box-direction: normal;
      -ms-flex-direction: row;
          flex-direction: row;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
}

There is currently no support for preprocessors such as Less, or for sharing variables across CSS files.

⁠Adding Images and Fonts

With Webpack, using static assets like images and fonts works similarly to CSS.

You can import an image right in a JavaScript module. This tells Webpack to include that image in the bundle. Unlike CSS imports, importing an image or a font gives you a string value. This value is the final image path you can reference in your code.

Here is an example:

import React from 'react';
import logo from './logo.png'; // Tell Webpack this JS file uses this image

console.log(logo); // /logo.84287d09.png

function Header() {
  // Import result is the URL of your image
  return <img src={logo} alt="Logo" />;
}

export default function Header;

This ensures that when the project is built, Webpack will correctly move the images into the build folder, and provide us with correct paths.

This works in CSS too:

.Logo {
  background-image: url(./logo.png);
}

Webpack finds all relative module references in CSS (they start with ./) and replaces them with the final paths from the compiled bundle. If you make a typo or accidentally delete an important file, you will see a compilation error, just like when you import a non-existent JavaScript module. The final filenames in the compiled bundle are generated by Webpack from content hashes. If the file content changes in the future, Webpack will give it a different name in production so you don’t need to worry about long-term caching of assets.

Please be advised that this is also a custom feature of Webpack.

It is not required for React but many people enjoy it (and React Native uses a similar mechanism for images).
An alternative way of handling static assets is described in the next section.

⁠Using the public Folder

Normally we encourage you to import assets in JavaScript files as described above. This mechanism provides a number of benefits:

• Scripts and stylesheets get minified and bundled together to avoid extra network requests.
• Missing files cause compilation errors instead of 404 errors for your users.
• Result filenames include content hashes so you don’t need to worry about browsers caching their old versions.

However there is an escape hatch that you can use to add an asset outside of the module system.

If you put a file into the public folder, it will not be processed by Webpack. Instead it will be copied into the build folder untouched. To reference assets in the public folder, you need to use a special variable called PUBLIC_URL.

Inside index.html, you can use it like this:

<link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">

Only files inside the public folder will be accessible by %PUBLIC_URL% prefix. If you need to use a file from src or node_modules, you’ll have to copy it there to explicitly specify your intention to make this file a part of the build.

When you run npm run build, Create React App will substitute %PUBLIC_URL% with a correct absolute path so your project works even if you use client-side routing or host it at a non-root URL.

In JavaScript code, you can use process.env.PUBLIC_URL for similar purposes:

render() {
  // Note: this is an escape hatch and should be used sparingly!
  // Normally we recommend using `import` for getting asset URLs
  // as described in “Adding Images and Fonts” above this section.
  return <img src={process.env.PUBLIC_URL + '/img/logo.png'} />;
}

Keep in mind the downsides of this approach:

• None of the files in public folder get post-processed or minified.
• Missing files will not be called at compilation time, and will cause 404 errors for your users.
• Result filenames won’t include content hashes so you’ll need to add query arguments or rename them every time they change.

However, it can be handy for referencing assets like manifest.webmanifest⁠ from HTML, or including small scripts like pace.js⁠ outside of the bundled code.

⁠Adding Bootstrap

You don’t have to use React Bootstrap⁠ together with React but it is a popular library for integrating Bootstrap with React apps. If you need it, you can integrate it with Create React App by following these steps:

Install React Bootstrap and Bootstrap from NPM. React Bootstrap does not include Bootstrap CSS so this needs to be installed as well:

npm install react-bootstrap --save
npm install bootstrap@3 --save

Import Bootstrap CSS and optionally Bootstrap theme CSS in the src/index.js file:

import 'bootstrap/dist/css/bootstrap.css';
import 'bootstrap/dist/css/bootstrap-theme.css';

Import required React Bootstrap components within src/App.js file or your custom component files:

import { Navbar, Jumbotron, Button } from 'react-bootstrap';

Now you are ready to use the imported React Bootstrap components within your component hierarchy defined in the render method. Here is an example App.js⁠ redone using React Bootstrap.

⁠Adding Flow

Flow typing is currently not supported out of the box⁠ with the default .flowconfig generated by Flow. If you run it, you might get errors like this:

node_modules/fbjs/lib/Deferred.js.flow:60
 60:     Promise.prototype.done.apply(this._promise, arguments);
                           ^^^^ property `done`. Property not found in
495: declare class Promise<+R> {
     ^ Promise. See lib: /private/tmp/flow/flowlib_34952d31/core.js:495

node_modules/fbjs/lib/shallowEqual.js.flow:29
 29:     return x !== 0 || 1 / (x: $FlowIssue) === 1 / (y: $FlowIssue);
                                   ^^^^^^^^^^ identifier `$FlowIssue`. Could not resolve name

To fix this, change your .flowconfig to look like this:

[ignore]
<PROJECT_ROOT>/node_modules/fbjs/.*

Re-run flow, and you shouldn’t get any extra issues.

⁠Adding Custom Environment Variables

Your project can consume variables declared in your environment as if they were declared locally in your JS files. By default you will have NODE_ENV defined for you, and any other environment variables starting with REACT_APP_. These environment variables will be defined for you on process.env. For example, having an environment variable named REACT_APP_SECRET_CODE will be exposed in your JS as process.env.REACT_APP_SECRET_CODE, in addition to process.env.NODE_ENV.

These environment variables can be useful for displaying information conditionally based on where the project is deployed or consuming sensitive data that lives outside of version control.

First, you need to have environment variables defined. For example, let’s say you wanted to consume a secret defined in the environment inside a <form>:

render() {
  return (
    <div>
      <small>You are running this application in <b>{process.env.NODE_ENV}</b> mode.</small>
      <form>
        <input type="hidden" defaultValue={process.env.REACT_APP_SECRET_CODE} />
      </form>
    </div>
  );
}

During the build, process.env.REACT_APP_SECRET_CODE will be replaced with the current value of the REACT_APP_SECRET_CODE environment variable. Remember that the NODE_ENV variable will be set for you automatically.

When you load the app in the browser and inspect the <input>, you will see its value set to abcdef, and the bold text will show the environment provided when using npm start:

<div>
  <small>You are running this application in <b>development</b> mode.</small>
  <form>
    <input type="hidden" value="abcdef" />
  </form>
</div>

Having access to the NODE_ENV is also useful for performing actions conditionally:

if (process.env.NODE_ENV !== 'production') {
  analytics.disable();
}

The above form is looking for a variable called REACT_APP_SECRET_CODE from the environment. In order to consume this value, we need to have it defined in the environment. This can be done using two ways: either in your shell or in a .env file.

⁠Adding Temporary Environment Variables In Your Shell

Defining environment variables can vary between OSes. It's also important to know that this manner is temporary for the life of the shell session.

⁠Windows (cmd.exe)

set REACT_APP_SECRET_CODE=abcdef&&npm start

(Note: the lack of whitespace is intentional.)

⁠Linux, OS X (Bash)

REACT_APP_SECRET_CODE=abcdef npm start

⁠Adding Development Environment Variables In .env

To define permanent environment variables, create a file called .env in the root of your project:

REACT_APP_SECRET_CODE=abcdef

These variables will act as the defaults if the machine does not explicitly set them.
Please refer to the dotenv documentation⁠ for more details.

⁠Can I Use Decorators?

Many popular libraries use decorators⁠ in their documentation.
Create React App doesn’t support decorator syntax at the moment because:

• It is an experimental proposal and is subject to change.
• The current specification version is not officially supported by Babel.
• If the specification changes, we won’t be able to write a codemod because we don’t use them internally at Facebook.

However in many cases you can rewrite decorator-based code without decorators just as fine.
Please refer to these two threads for reference:

• #214⁠
• #411⁠

Create React App will add decorator support when the specification advances to a stable stage.

⁠Integrating with a Node Backend

Check out this tutorial⁠ for instructions on integrating an app with a Node backend running on another port, and using fetch() to access it. You can find the companion GitHub repository here⁠.

⁠Proxying API Requests in Development

People often serve the front-end React app from the same host and port as their backend implementation.
For example, a production setup might look like this after the app is deployed:

/             - static server returns index.html with React app
/todos        - static server returns index.html with React app
/api/todos    - server handles any /api/* requests using the backend implementation

Such setup is not required. However, if you do have a setup like this, it is convenient to write requests like fetch('/api/todos') without worrying about redirecting them to another host or port during development.

To tell the development server to proxy any unknown requests to your API server in development, add a proxy field to your package.json, for example:

  "proxy": "http://localhost:4000",

This way, when you fetch('/api/todos') in development, the development server will recognize that it’s not a static asset, and will proxy your request to http://localhost:4000/api/todos as a fallback. The development server will only attempt to send requests without a text/html accept header to the proxy.

Conveniently, this avoids CORS issues⁠ and error messages like this in development:

Fetch API cannot load http://localhost:4000/api/todos. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Keep in mind that proxy only has effect in development (with npm start), and it