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This project was bootstrapped with [Create React App](
# What's Open Web
Below you will find some information on how to perform common tasks.<br>
You can find the most recent version of this guide [here](
What's Open Web is a React application that uses data retrieved from
the [What's Open API]( to display information about the facilities on
George Mason University's campuses.
## Table of Contents
## Contributing
- Join `#whats-open-web` on [slack](
- Tag a fixed issue within the commit by ending the commit with `closes #issue`
- Open issues can be found [here](
- [Updating to New Releases](#updating-to-new-releases)
- [Sending Feedback](#sending-feedback)
- [Folder Structure](#folder-structure)
- [Available Scripts](#available-scripts)
- [npm start](#npm-start)
- [npm test](#npm-test)
- [npm run build](#npm-run-build)
- [npm run eject](#npm-run-eject)
- [Supported Language Features and Polyfills](#supported-language-features-and-polyfills)
- [Syntax Highlighting in the Editor](#syntax-highlighting-in-the-editor)
- [Displaying Lint Output in the Editor](#displaying-lint-output-in-the-editor)
- [Debugging in the Editor](#debugging-in-the-editor)
- [Formatting Code Automatically](#formatting-code-automatically)
- [Changing the Page `<title>`](#changing-the-page-title)
- [Installing a Dependency](#installing-a-dependency)
- [Importing a Component](#importing-a-component)
- [Code Splitting](#code-splitting)
- [Adding a Stylesheet](#adding-a-stylesheet)
- [Post-Processing CSS](#post-processing-css)
- [Adding a CSS Preprocessor (Sass, Less etc.)](#adding-a-css-preprocessor-sass-less-etc)
- [Adding Images, Fonts, and Files](#adding-images-fonts-and-files)
- [Using the `public` Folder](#using-the-public-folder)
- [Changing the HTML](#changing-the-html)
- [Adding Assets Outside of the Module System](#adding-assets-outside-of-the-module-system)
- [When to Use the `public` Folder](#when-to-use-the-public-folder)
- [Using Global Variables](#using-global-variables)
- [Adding Bootstrap](#adding-bootstrap)
- [Using a Custom Theme](#using-a-custom-theme)
- [Adding Flow](#adding-flow)
- [Adding Custom Environment Variables](#adding-custom-environment-variables)
- [Referencing Environment Variables in the HTML](#referencing-environment-variables-in-the-html)
- [Adding Temporary Environment Variables In Your Shell](#adding-temporary-environment-variables-in-your-shell)
- [Adding Development Environment Variables In `.env`](#adding-development-environment-variables-in-env)
- [Can I Use Decorators?](#can-i-use-decorators)
- [Integrating with an API Backend](#integrating-with-an-api-backend)
- [Node](#node)
- [Ruby on Rails](#ruby-on-rails)
- [Proxying API Requests in Development](#proxying-api-requests-in-development)
- ["Invalid Host Header" Errors After Configuring Proxy](#invalid-host-header-errors-after-configuring-proxy)
- [Configuring the Proxy Manually](#configuring-the-proxy-manually)
- [Configuring a WebSocket Proxy](#configuring-a-websocket-proxy)
- [Using HTTPS in Development](#using-https-in-development)
- [Generating Dynamic `<meta>` Tags on the Server](#generating-dynamic-meta-tags-on-the-server)
- [Pre-Rendering into Static HTML Files](#pre-rendering-into-static-html-files)
- [Injecting Data from the Server into the Page](#injecting-data-from-the-server-into-the-page)
- [Running Tests](#running-tests)
- [Filename Conventions](#filename-conventions)
- [Command Line Interface](#command-line-interface)
- [Version Control Integration](#version-control-integration)
- [Writing Tests](#writing-tests)
- [Testing Components](#testing-components)
- [Using Third Party Assertion Libraries](#using-third-party-assertion-libraries)
- [Initializing Test Environment](#initializing-test-environment)
- [Focusing and Excluding Tests](#focusing-and-excluding-tests)
- [Coverage Reporting](#coverage-reporting)
- [Continuous Integration](#continuous-integration)
- [Disabling jsdom](#disabling-jsdom)
- [Snapshot Testing](#snapshot-testing)
- [Editor Integration](#editor-integration)
- [Developing Components in Isolation](#developing-components-in-isolation)
- [Getting Started with Storybook](#getting-started-with-storybook)
- [Getting Started with Styleguidist](#getting-started-with-styleguidist)
- [Making a Progressive Web App](#making-a-progressive-web-app)
- [Offline-First Considerations](#offline-first-considerations)
- [Progressive Web App Metadata](#progressive-web-app-metadata)
- [Analyzing the Bundle Size](#analyzing-the-bundle-size)
- [Deployment](#deployment)
- [Static Server](#static-server)
- [Other Solutions](#other-solutions)
- [Serving Apps with Client-Side Routing](#serving-apps-with-client-side-routing)
- [Building for Relative Paths](#building-for-relative-paths)
- [Azure](#azure)
- [Firebase](#firebase)
- [GitHub Pages](#github-pages)
- [Heroku](#heroku)
- [Modulus](#modulus)
- [Netlify](#netlify)
- [Now](#now)
- [S3 and CloudFront](#s3-and-cloudfront)
- [Surge](#surge)
- [Advanced Configuration](#advanced-configuration)
- [Troubleshooting](#troubleshooting)
- [`npm start` doesn’t detect changes](#npm-start-doesnt-detect-changes)
- [`npm test` hangs on macOS Sierra](#npm-test-hangs-on-macos-sierra)
- [`npm run build` exits too early](#npm-run-build-exits-too-early)
- [`npm run build` fails on Heroku](#npm-run-build-fails-on-heroku)
- [Moment.js locales are missing](#momentjs-locales-are-missing)
- [Something Missing?](#something-missing)
### Requirements
- [git](
- [npm]( or [yarn](
## Updating to New Releases
### Setup
1. Clone the repository
2. Install dependencies either by `npm install` or `yarn`
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:
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.<br>
You need to **put any JS and CSS files inside `src`**, otherwise Webpack won’t see them.
Only files inside `public` can be used from `public/index.html`.<br>
Read instructions below for using assets from JavaScript and HTML.
You can, however, create more top-level directories.<br>
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.<br>
Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
The page will reload if you make edits.<br>
You will also see any lint errors in the console.
### `npm test`
Launches the test runner in the interactive watch mode.<br>
See the section about [running tests](#running-tests) for more information.
### `npm run build`
Builds the app for production to the `build` folder.<br>
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.<br>
Your app is ready to be deployed!
See the section about [deployment](#deployment) for more information.
### `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.
## Supported Language Features and Polyfills
This project supports a superset of the latest JavaScript standard.<br>
In addition to [ES6]( syntax features, it also supports:
* [Exponentiation Operator]( (ES2016).
* [Async/await]( (ES2017).
* [Object Rest/Spread Properties]( (stage 3 proposal).
* [Dynamic import()]( (stage 3 proposal)
* [Class Fields and Static Properties]( (stage 2 proposal).
* [JSX]( and [Flow]( syntax.
Learn more about [different proposal stages](
While we recommend to use experimental proposals with some caution, Facebook heavily uses these features in the product code, so we intend to provide [codemods]( if any of these proposals change in the future.
Note that **the project only includes a few ES6 [polyfills](**:
* [`Object.assign()`]( via [`object-assign`](
* [`Promise`]( via [`promise`](
* [`fetch()`]( via [`whatwg-fetch`](
If you use any other ES6+ features that need **runtime support** (such as `Array.from()` or `Symbol`), make sure you are including the appropriate polyfills manually, or that the browsers you are targeting already support them.
## Syntax Highlighting in the Editor
To configure the syntax highlighting in your favorite text editor, head to the [relevant Babel documentation page]( and follow the instructions. Some of the most popular editors are covered.
## Displaying Lint Output in the Editor
>Note: this feature is available with `react-scripts@0.2.0` and higher.<br>
>It also only works with npm 3 or higher.
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 a file called `.eslintrc` to the project root:
"extends": "react-app"
Now your editor should report the linting warnings.
Note that even if you edit your `.eslintrc` file further, these changes will **only affect the editor integration**. They won’t affect the terminal and in-browser lint output. This is because Create React App intentionally provides a minimal set of rules that find common mistakes.
If you want to enforce a coding style for your project, consider using [Prettier]( instead of ESLint style rules.
## Debugging in the Editor
**This feature is currently only supported by [Visual Studio Code]( editor.**
Visual Studio Code supports debugging out of the box with Create React App. This enables you as a developer to write and debug your React code without leaving the editor, and most importantly it enables you to have a continuous development workflow, where context switching is minimal, as you don’t have to switch between tools.
You would need to have the latest version of [VS Code]( and VS Code [Chrome Debugger Extension]( installed.
Then add the block below to your `launch.json` file and put it inside the `.vscode` folder in your app’s root directory.
"version": "0.2.0",
"configurations": [{
"name": "Chrome",
"type": "chrome",
"request": "launch",
"url": "http://localhost:3000",
"webRoot": "${workspaceRoot}/src",
"userDataDir": "${workspaceRoot}/.vscode/chrome",
"sourceMapPathOverrides": {
"webpack:///src/*": "${webRoot}/*"
Start your app by running `npm start`, and start debugging in VS Code by pressing `F5` or by clicking the green debug icon. You can now write code, set breakpoints, make changes to the code, and debug your newly modified code—all from your editor.
## Formatting Code Automatically
Prettier is an opinionated code formatter with support for JavaScript, CSS and JSON. With Prettier you can format the code you write automatically to ensure a code style within your project. See the [Prettier's GitHub page]( for more information, and look at this [page to see it in action](
To format our code whenever we make a commit in git, we need to install the following dependencies:
npm install --save husky lint-staged prettier
Alternatively you may use `yarn`:
yarn add husky lint-staged prettier
* `husky` makes it easy to use githooks as if they are npm scripts.
* `lint-staged` allows us to run scripts on staged files in git. See this [blog post about lint-staged to learn more about it](
* `prettier` is the JavaScript formatter we will run before commits.
Now we can make sure every file is formatted correctly by adding a few lines to the `package.json` in the project root.
Add the following line to `scripts` section:
"scripts": {
+ "precommit": "lint-staged",
"start": "react-scripts start",
"build": "react-scripts build",
Next we add a 'lint-staged' field to the `package.json`, for example:
"dependencies": {
// ...
+ "lint-staged": {
+ "src/**/*.{js,jsx,json,css}": [
+ "prettier --single-quote --write",
+ "git add"
+ ]
+ },
"scripts": {
Now, whenever you make a commit, Prettier will format the changed files automatically. You can also run `./node_modules/.bin/prettier --single-quote --write "src/**/*.{js,jsx}"` to format your entire project for the first time.
Next you might want to integrate Prettier in your favorite editor. Read the section on [Editor Integration]( on the Prettier GitHub page.
## Changing the Page `<title>`
You can find the source HTML file in the `public` folder of the generated project. You may edit the `<title>` tag in it to change the title from “React App” to anything else.
Note that normally you wouldn’t edit files in the `public` folder very often. For example, [adding a stylesheet](#adding-a-stylesheet) is done without touching the HTML.
If you need to dynamically update the page title based on the content, you can use the browser [`document.title`]( API. For more complex scenarios when you want to change the title from React components, you can use [React Helmet](, a third party library.
If you use a custom server for your app in production and want to modify the title before it gets sent to the browser, you can follow advice in [this section](#generating-dynamic-meta-tags-on-the-server). Alternatively, you can pre-build each page as a static HTML file which then loads the JavaScript bundle, which is covered [here](#pre-rendering-into-static-html-files).
## 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 react-router
Alternatively you may use `yarn`:
yarn add react-router
This works for any library, not just `react-router`.
## Importing a Component
This project setup supports ES6 modules thanks to Babel.<br>
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](
## Code Splitting
Instead of downloading the entire app before users can use it, code splitting allows you to split your code into small chunks which you can then load on demand.
This project setup supports code splitting via [dynamic `import()`]( Its [proposal]( is in stage 3. The `import()` function-like form takes the module name as an argument and returns a [`Promise`]( which always resolves to the namespace object of the module.
Here is an example:
### `moduleA.js`
const moduleA = 'Hello';
export { moduleA };
### `App.js`
import React, { Component } from 'react';
class App extends Component {
handleClick = () => {
.then(({ moduleA }) => {
// Use moduleA
.catch(err => {
// Handle failure
render() {
return (
<button onClick={this.handleClick}>Load</button>
export default App;
This will make `moduleA.js` and all its unique dependencies as a separate chunk that only loads after the user clicks the 'Load' button.
You can also use it with `async` / `await` syntax if you prefer it.
### With React Router
If you are using React Router check out [this tutorial]( on how to use code splitting with it. You can find the companion GitHub repository [here](
## 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;
If you need to disable autoprefixing for some reason, [follow this section](
## Adding a CSS Preprocessor (Sass, Less etc.)
Generally, we recommend that you don’t reuse the same CSS classes across different components. For example, instead of using a `.Button` CSS class in `<AcceptButton>` and `<RejectButton>` components, we recommend creating a `<Button>` component with its own `.Button` styles, that both `<AcceptButton>` and `<RejectButton>` can render (but [not inherit](
Following this rule often makes CSS preprocessors less useful, as features like mixins and nesting are replaced by component composition. You can, however, integrate a CSS preprocessor if you find it valuable. In this walkthrough, we will be using Sass, but you can also use Less, or another alternative.
First, let’s install the command-line interface for Sass:
npm install --save node-sass-chokidar
Alternatively you may use `yarn`:
yarn add node-sass-chokidar
Then in `package.json`, add the following lines to `scripts`:
"scripts": {
+ "build-css": "node-sass-chokidar src/ -o src/",
+ "watch-css": "npm run build-css && node-sass-chokidar src/ -o src/ --watch --recursive",
"start": "react-scripts start",
"build": "react-scripts build",
"test": "react-scripts test --env=jsdom",
>Note: To use a different preprocessor, replace `build-css` and `watch-css` commands according to your preprocessor’s documentation.
Now you can rename `src/App.css` to `src/App.scss` and run `npm run watch-css`. The watcher will find every Sass file in `src` subdirectories, and create a corresponding CSS file next to it, in our case overwriting `src/App.css`. Since `src/App.js` still imports `src/App.css`, the styles become a part of your application. You can now edit `src/App.scss`, and `src/App.css` will be regenerated.
To share variables between Sass files, you can use Sass imports. For example, `src/App.scss` and other component style files could include `@import "./shared.scss";` with variable definitions.
To enable importing files without using relative paths, you can add the `--include-path` option to the command in `package.json`.
"build-css": "node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/",
"watch-css": "npm run build-css && node-sass-chokidar --include-path ./src --include-path ./node_modules src/ -o src/ --watch --recursive",
This will allow you to do imports like
@import 'styles/_colors.scss'; // assuming a styles directory under src/
@import 'nprogress/nprogress'; // importing a css file from the nprogress node module
At this point you might want to remove all CSS files from the source control, and add `src/**/*.css` to your `.gitignore` file. It is generally a good practice to keep the build products outside of the source control.
As a final step, you may find it convenient to run `watch-css` automatically with `npm start`, and run `build-css` as a part of `npm run build`. You can use the `&&` operator to execute two scripts sequentially. However, there is no cross-platform way to run two scripts in parallel, so we will install a package for this:
npm install --save npm-run-all
Alternatively you may use `yarn`:
yarn add npm-run-all
Then we can change `start` and `build` scripts to include the CSS preprocessor commands:
"scripts": {
"build-css": "node-sass-chokidar src/ -o src/",
"watch-css": "npm run build-css && node-sass-chokidar src/ -o src/ --watch --recursive",
- "start": "react-scripts start",
- "build": "react-scripts build",
+ "start-js": "react-scripts start",
+ "start": "npm-run-all -p watch-css start-js",
+ "build": "npm run build-css && react-scripts build",
"test": "react-scripts test --env=jsdom",
"eject": "react-scripts eject"
Now running `npm start` and `npm run build` also builds Sass files.
**Why `node-sass-chokidar`?**
`node-sass` has been reported as having the following issues:
- `node-sass --watch` has been reported to have *performance issues* in certain conditions when used in a virtual machine or with docker.
- Infinite styles compiling [#1939](
- `node-sass` has been reported as having issues with detecting new files in a directory [#1891](
`node-sass-chokidar` is used here as it addresses these issues.
## Adding Images, Fonts, and Files
With Webpack, using static assets like images and fonts works similarly to CSS.
You can **`import` a file right in a JavaScript module**. This tells Webpack to include that file in the bundle. Unlike CSS imports, importing a file gives you a string value. This value is the final path you can reference in your code, e.g. as the `src` attribute of an image or the `href` of a link to a PDF.
To reduce the number of requests to the server, importing images that are less than 10,000 bytes returns a [data URI]( instead of a path. This applies to the following file extensions: bmp, gif, jpg, jpeg, and png. SVG files are excluded due to [#1153](
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