README.md

  expect(wrapper.contains(welcome)).toEqual(true);
});
```

All Jest matchers are [extensively documented here](http://facebook.github.io/jest/docs/expect.html).<br>
Nevertheless you can use a third-party assertion library like [Chai](http://chaijs.com/) if you want to, as described below.

Additionally, you might find [jest-enzyme](https://github.com/blainekasten/enzyme-matchers) helpful to simplify your tests with readable matchers. The above `contains` code can be written simpler with jest-enzyme.

```js
expect(wrapper).toContainReact(welcome)
```

To setup jest-enzyme with Create React App, follow the instructions for [initializing your test environment](#initializing-test-environment) to import `jest-enzyme`.

```sh
npm install --save-dev jest-enzyme
```

```js
// src/setupTests.js
import 'jest-enzyme';
```


### Using Third Party Assertion Libraries

We recommend that you use `expect()` for assertions and `jest.fn()` for spies. If you are having issues with them please [file those against Jest](https://github.com/facebook/jest/issues/new), and we’ll fix them. We intend to keep making them better for React, supporting, for example, [pretty-printing React elements as JSX](https://github.com/facebook/jest/pull/1566).

However, if you are used to other libraries, such as [Chai](http://chaijs.com/) and [Sinon](http://sinonjs.org/), or if you have existing code using them that you’d like to port over, you can import them normally like this:

```js
import sinon from 'sinon';
import { expect } from 'chai';
```

and then use them in your tests like you normally do.

### Initializing Test Environment

>Note: this feature is available with `react-scripts@0.4.0` and higher.

If your app uses a browser API that you need to mock in your tests or if you just need a global setup before running your tests, add a `src/setupTests.js` to your project. It will be automatically executed before running your tests.

For example:

#### `src/setupTests.js`
```js
const localStorageMock = {
  getItem: jest.fn(),
  setItem: jest.fn(),
  clear: jest.fn()
};
global.localStorage = localStorageMock
```

### Focusing and Excluding Tests

You can replace `it()` with `xit()` to temporarily exclude a test from being executed.<br>
Similarly, `fit()` lets you focus on a specific test without running any other tests.

### Coverage Reporting

Jest has an integrated coverage reporter that works well with ES6 and requires no configuration.<br>
Run `npm test -- --coverage` (note extra `--` in the middle) to include a coverage report like this:

![coverage report](http://i.imgur.com/5bFhnTS.png)

Note that tests run much slower with coverage so it is recommended to run it separately from your normal workflow.

### Continuous Integration

By default `npm test` runs the watcher with interactive CLI. However, you can force it to run tests once and finish the process by setting an environment variable called `CI`.

When creating a build of your application with `npm run build` linter warnings are not checked by default. Like `npm test`, you can force the build to perform a linter warning check by setting the environment variable `CI`. If any warnings are encountered then the build fails.

Popular CI servers already set the environment variable `CI` by default but you can do this yourself too:

### On CI servers
#### Travis CI

1. Following the [Travis Getting started](https://docs.travis-ci.com/user/getting-started/) guide for syncing your GitHub repository with Travis.  You may need to initialize some settings manually in your [profile](https://travis-ci.org/profile) page.
1. Add a `.travis.yml` file to your git repository.
```
language: node_js
node_js:
  - 4
  - 6
cache:
  directories:
    - node_modules
script:
  - npm test
  - npm run build
```
1. Trigger your first build with a git push.
1. [Customize your Travis CI Build](https://docs.travis-ci.com/user/customizing-the-build/) if needed.

### On your own environment
##### Windows (cmd.exe)

```cmd
set CI=true&&npm test
```

```cmd
set CI=true&&npm run build
```

(Note: the lack of whitespace is intentional.)

##### Linux, macOS (Bash)

```bash
CI=true npm test
```

```bash
CI=true npm run build
```

The test command will force Jest to run tests once instead of launching the watcher.

>  If you find yourself doing this often in development, please [file an issue](https://github.com/facebookincubator/create-react-app/issues/new) to tell us about your use case because we want to make watcher the best experience and are open to changing how it works to accommodate more workflows.

The build command will check for linter warnings and fail if any are found.

### Disabling jsdom

By default, the `package.json` of the generated project looks like this:

```js
  // ...
  "scripts": {
    // ...
    "test": "react-scripts test --env=jsdom"
  }
```

If you know that none of your tests depend on [jsdom](https://github.com/tmpvar/jsdom), you can safely remove `--env=jsdom`, and your tests will run faster.<br>
To help you make up your mind, here is a list of APIs that **need jsdom**:

* Any browser globals like `window` and `document`
* [`ReactDOM.render()`](https://facebook.github.io/react/docs/top-level-api.html#reactdom.render)
* [`TestUtils.renderIntoDocument()`](https://facebook.github.io/react/docs/test-utils.html#renderintodocument) ([a shortcut](https://github.com/facebook/react/blob/34761cf9a252964abfaab6faf74d473ad95d1f21/src/test/ReactTestUtils.js#L83-L91) for the above)
* [`mount()`](http://airbnb.io/enzyme/docs/api/mount.html) in [Enzyme](http://airbnb.io/enzyme/index.html)

In contrast, **jsdom is not needed** for the following APIs:

* [`TestUtils.createRenderer()`](https://facebook.github.io/react/docs/test-utils.html#shallow-rendering) (shallow rendering)
* [`shallow()`](http://airbnb.io/enzyme/docs/api/shallow.html) in [Enzyme](http://airbnb.io/enzyme/index.html)

Finally, jsdom is also not needed for [snapshot testing](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html).

### Snapshot Testing

Snapshot testing is a feature of Jest that automatically generates text snapshots of your components and saves them on the disk so if the UI output changes, you get notified without manually writing any assertions on the component output. [Read more about snapshot testing.](http://facebook.github.io/jest/blog/2016/07/27/jest-14.html)

### Editor Integration

If you use [Visual Studio Code](https://code.visualstudio.com), there is a [Jest extension](https://github.com/orta/vscode-jest) which works with Create React App out of the box. This provides a lot of IDE-like features while using a text editor: showing the status of a test run with potential fail messages inline, starting and stopping the watcher automatically, and offering one-click snapshot updates.

![VS Code Jest Preview](https://cloud.githubusercontent.com/assets/49038/20795349/a032308a-b7c8-11e6-9b34-7eeac781003f.png)

## Developing Components in Isolation

Usually, in an app, you have a lot of UI components, and each of them has many different states.
For an example, a simple button component could have following states:

* With a text label.
* With an emoji.
* In the disabled mode.

Usually, it’s hard to see these states without running a sample app or some examples.

Create React App doesn’t include any tools for this by default, but you can easily add [React Storybook](https://github.com/kadirahq/react-storybook) to your project. **It is a third-party tool that lets you develop components and see all their states in isolation from your app**.

![React Storybook Demo](http://i.imgur.com/7CIAWpB.gif)

You can also deploy your Storybook as a static app. This way, everyone in your team can view and review different states of UI components without starting a backend server or creating an account in your app.

**Here’s how to setup your app with Storybook:**

First, install the following npm package globally:

```sh
npm install -g getstorybook
```

Then, run the following command inside your app’s directory:

```sh
getstorybook
```

After that, follow the instructions on the screen.

Learn more about React Storybook:

* Screencast: [Getting Started with React Storybook](https://egghead.io/lessons/react-getting-started-with-react-storybook)
* [GitHub Repo](https://github.com/kadirahq/react-storybook)
* [Documentation](https://getstorybook.io/docs)
* [Snapshot Testing](https://github.com/kadirahq/storyshots) with React Storybook

## Making a Progressive Web App

You can turn your React app into a [Progressive Web App](https://developers.google.com/web/progressive-web-apps/) by following the steps in [this repository](https://github.com/jeffposnick/create-react-pwa).

## Deployment

`npm run build` creates a `build` directory with a production build of your app. Set up your favourite HTTP server so that a visitor to your site is served `index.html`, and requests to static paths like `/static/js/main.<hash>.js` are served with the contents of the `/static/js/main.<hash>.js` file. For example, Python contains a built-in HTTP server that can serve static files:

```sh
cd build
python -m SimpleHTTPServer 9000
```

If you’re using [Node](https://nodejs.org/) and [Express](http://expressjs.com/) as a server, it might look like this:

```javascript
const express = require('express');
const path = require('path');
const app = express();

app.use(express.static('./build'));

app.get('/', function (req, res) {
  res.sendFile(path.join(__dirname, './build', 'index.html'));
});

app.listen(9000);
```

Create React App is not opinionated about your choice of web server. Any static file server will do. The `build` folder with static assets is the only output produced by Create React App.

However this is not quite enough if you use client-side routing. Read the next section if you want to support URLs like `/todos/42` in your single-page app.

### Serving Apps with Client-Side Routing

If you use routers that use the HTML5 [`pushState` history API](https://developer.mozilla.org/en-US/docs/Web/API/History_API#Adding_and_modifying_history_entries) under the hood (for example, [React Router](https://github.com/ReactTraining/react-router) with `browserHistory`), many static file servers will fail. For example, if you used React Router with a route for `/todos/42`, the development server will respond to `localhost:3000/todos/42` properly, but an Express serving a production build as above will not.

This is because when there is a fresh page load for a `/todos/42`, the server looks for the file `build/todos/42` and does not find it. The server needs to be configured to respond to a request to `/todos/42` by serving `index.html`. For example, we can amend our Express example above to serve `index.html` for any unknown paths:

```diff
 app.use(express.static('./build'));

-app.get('/', function (req, res) {
+app.get('/*', function (req, res) {
   res.sendFile(path.join(__dirname, './build', 'index.html'));
 });
```

If you’re using [Apache](https://httpd.apache.org/), you need to create a `.htaccess` file in the `public` folder that looks like this:

```
    Options -MultiViews
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.html [QSA,L]
```

It will get copied to the `build` folder when you run `npm run build`.

Now requests to `/todos/42` will be handled correctly both in development and in production.

### Building for Relative Paths

By default, Create React App produces a build assuming your app is hosted at the server root.<br>
To override this, specify the `homepage` in your `package.json`, for example:

```js
  "homepage": "http://mywebsite.com/relativepath",
```

This will let Create React App correctly infer the root path to use in the generated HTML file.

#### Serving the Same Build from Different Paths

>Note: this feature is available with `react-scripts@0.9.0` and higher.

If you are not using the HTML5 `pushState` history API or not using client-side routing at all, it is unnecessary to specify the URL from which your app will be served. Instead, you can put this in your `package.json`:

```js
  "homepage": ".",
```

This will make sure that all the asset paths are relative to `index.html`. You will then be able to move your app from `http://mywebsite.com` to `http://mywebsite.com/relativepath` or even `http://mywebsite.com/relative/path` without having to rebuild it.

### Azure

See [this](https://medium.com/@to_pe/deploying-create-react-app-on-microsoft-azure-c0f6686a4321) blog post on how to deploy your React app to [Microsoft Azure](https://azure.microsoft.com/).

### Firebase

Install the Firebase CLI if you haven’t already by running `npm install -g firebase-tools`. Sign up for a [Firebase account](https://console.firebase.google.com/) and create a new project. Run `firebase login` and login with your previous created Firebase account.

Then run the `firebase init` command from your project’s root. You need to choose the **Hosting: Configure and deploy Firebase Hosting sites** and choose the Firebase project you created in the previous step. You will need to agree with `database.rules.json` being created, choose `build` as the public directory, and also agree to **Configure as a single-page app** by replying with `y`.

```sh
    === Project Setup

    First, let's associate this project directory with a Firebase project.
    You can create multiple project aliases by running firebase use --add,
    but for now we'll just set up a default project.

    ? What Firebase project do you want to associate as default? Example app (example-app-fd690)

    === Database Setup

    Firebase Realtime Database Rules allow you to define how your data should be
    structured and when your data can be read from and written to.

    ? What file should be used for Database Rules? database.rules.json
    ✔  Database Rules for example-app-fd690 have been downloaded to database.rules.json.
    Future modifications to database.rules.json will update Database Rules when you run
    firebase deploy.

    === Hosting Setup

    Your public directory is the folder (relative to your project directory) that
    will contain Hosting assets to uploaded with firebase deploy. If you
    have a build process for your assets, use your build's output directory.

    ? What do you want to use as your public directory? build
    ? Configure as a single-page app (rewrite all urls to /index.html)? Yes
    ✔  Wrote build/index.html

    i  Writing configuration info to firebase.json...
    i  Writing project information to .firebaserc...

    ✔  Firebase initialization complete!
```

Now, after you create a production build with `npm run build`, you can deploy it by running `firebase deploy`.

```sh
    === Deploying to 'example-app-fd690'...

    i  deploying database, hosting
    ✔  database: rules ready to deploy.
    i  hosting: preparing build directory for upload...
    Uploading: [==============================          ] 75%✔  hosting: build folder uploaded successfully
    ✔  hosting: 8 files uploaded successfully
    i  starting release process (may take several minutes)...

    ✔  Deploy complete!

    Project Console: https://console.firebase.google.com/project/example-app-fd690/overview
    Hosting URL: https://example-app-fd690.firebaseapp.com
```

For more information see [Add Firebase to your JavaScript Project](https://firebase.google.com/docs/web/setup).

### GitHub Pages

>Note: this feature is available with `react-scripts@0.2.0` and higher.

#### Step 1: Add `homepage` to `package.json`

**The step below is important!**<br>
**If you skip it, your app will not deploy correctly.**

Open your `package.json` and add a `homepage` field:

```js
  "homepage": "https://myusername.github.io/my-app",
```

Create React App uses the `homepage` field to determine the root URL in the built HTML file.

#### Step 2: Install `gh-pages` and add `deploy` to `scripts` in `package.json`

Now, whenever you run `npm run build`, you will see a cheat sheet with instructions on how to deploy to GitHub Pages.

To publish it at [https://myusername.github.io/my-app](https://myusername.github.io/my-app), run:

```sh
npm install --save-dev gh-pages
```

Add the following scripts in your `package.json`:

```js
  // ...
  "scripts": {
    // ...
    "predeploy": "npm run build",
    "deploy": "gh-pages -d build"
  }
```

The `predeploy` script will run automatically before `deploy` is run.

#### Step 3: Deploy the site by running `npm run deploy`

Then run:

```sh
npm run deploy
```

#### Step 4: Ensure your project’s settings use `gh-pages`

Finally, make sure **GitHub Pages** option in your GitHub project settings is set to use the `gh-pages` branch:

<img src="http://i.imgur.com/HUjEr9l.png" width="500" alt="gh-pages branch setting">

#### Step 5: Optionally, configure the domain

You can configure a custom domain with GitHub Pages by adding a `CNAME` file to the `public/` folder.

#### Notes on client-side routing

GitHub Pages doesn’t support routers that use the HTML5 `pushState` history API under the hood (for example, React Router using `browserHistory`). This is because when there is a fresh page load for a url like `http://user.github.io/todomvc/todos/42`, where `/todos/42` is a frontend route, the GitHub Pages server returns 404 because it knows nothing of `/todos/42`. If you want to add a router to a project hosted on GitHub Pages, here are a couple of solutions:

* You could switch from using HTML5 history API to routing with hashes. If you use React Router, you can switch to `hashHistory` for this effect, but the URL will be longer and more verbose (for example, `http://user.github.io/todomvc/#/todos/42?_k=yknaj`). [Read more](https://github.com/reactjs/react-router/blob/master/docs/guides/Histories.md#histories) about different history implementations in React Router.
* Alternatively, you can use a trick to teach GitHub Pages to handle 404 by redirecting to your `index.html` page with a special redirect parameter. You would need to add a `404.html` file with the redirection code to the `build` folder before deploying your project, and you’ll need to add code handling the redirect parameter to `index.html`. You can find a detailed explanation of this technique [in this guide](https://github.com/rafrex/spa-github-pages).

### Heroku

Use the [Heroku Buildpack for Create React App](https://github.com/mars/create-react-app-buildpack).<br>
You can find instructions in [Deploying React with Zero Configuration](https://blog.heroku.com/deploying-react-with-zero-configuration).

#### Resolving Heroku Deployment Errors

Sometimes `npm run build` works locally but fails during deploy via Heroku. Following are the most common cases.

##### "Module not found: Error: Cannot resolve 'file' or 'directory'"

If you get something like this:

```
remote: Failed to create a production build. Reason:
remote: Module not found: Error: Cannot resolve 'file' or 'directory'
MyDirectory in /tmp/build_1234/src
```

It means you need to ensure that the lettercase of the file or directory you `import` matches the one you see on your filesystem or on GitHub.

This is important because Linux (the operating system used by Heroku) is case sensitive. So `MyDirectory` and `mydirectory` are two distinct directories and thus, even though the project builds locally, the difference in case breaks the `import` statements on Heroku remotes.

##### "Could not find a required file."

If you exclude or ignore necessary files from the package you will see a error similar this one:

```
remote: Could not find a required file.
remote:   Name: `index.html`
remote:   Searched in: /tmp/build_a2875fc163b209225122d68916f1d4df/public
remote:
remote: npm ERR! Linux 3.13.0-105-generic
remote: npm ERR! argv "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/node" "/tmp/build_a2875fc163b209225122d68916f1d4df/.heroku/node/bin/npm" "run" "build"
```

In this case, ensure that the file is there with the proper lettercase and that’s not ignored on your local `.gitignore` or `~/.gitignore_global`.

### Modulus

See the [Modulus blog post](http://blog.modulus.io/deploying-react-apps-on-modulus) on how to deploy your react app to Modulus.

## Netlify

**To do a manual deploy to Netlify’s CDN:**

```sh
npm install netlify-cli
netlify deploy
```

Choose `build` as the path to deploy.

**To setup continuous delivery:**

With this setup Netlify will build and deploy when you push to git or open a pull request:

1. [Start a new netlify project](https://app.netlify.com/signup)
2. Pick your Git hosting service and select your repository
3. Click `Build your site`

**Support for client-side routing:**

To support `pushState`, make sure to create a `public/_redirects` file with the following rewrite rules:

```
/*  /index.html  200
```

When you build the project, Create React App will place the `public` folder contents into the build output.

### Now

[now](https://zeit.co/now) offers a zero-configuration single-command deployment.

1. Install the `now` command-line tool either via the recommended [desktop tool](https://zeit.co/download) or via node with `npm install -g now`.

2. Install `serve` by running `npm install --save serve`.

3. Add this line to `scripts` in `package.json`:
    
    ```
    "now-start": "serve build/",
    ```
    
4. Run `now` from your project directory. You will see a **now.sh** URL in your output like this:
    
    ```
    > Ready! https://your-project-dirname-tpspyhtdtk.now.sh (copied to clipboard)
    ```
    
    Paste that URL into your browser when the build is complete, and you will see your deployed app.

Details are available in [this article.](https://zeit.co/blog/now-static)

### S3 and CloudFront

See this [blog post](https://medium.com/@omgwtfmarc/deploying-create-react-app-to-s3-or-cloudfront-48dae4ce0af) on how to deploy your React app to Amazon Web Services [S3](https://aws.amazon.com/s3) and [CloudFront](https://aws.amazon.com/cloudfront/).

### Surge

Install the Surge CLI if you haven’t already by running `npm install -g surge`. Run the `surge` command and log in you or create a new account. You just need to specify the *build* folder and your custom domain, and you are done.

```sh
              email: email@domain.com
           password: ********
       project path: /path/to/project/build
               size: 7 files, 1.8 MB
             domain: create-react-app.surge.sh
             upload: [====================] 100%, eta: 0.0s
   propagate on CDN: [====================] 100%
               plan: Free
              users: email@domain.com
         IP Address: X.X.X.X

    Success! Project is published and running at create-react-app.surge.sh
```

Note that in order to support routers that use HTML5 `pushState` API, you may want to rename the `index.html` in your build folder to `200.html` before deploying to Surge. This [ensures that every URL falls back to that file](https://surge.sh/help/adding-a-200-page-for-client-side-routing).

## Advanced Configuration

You can adjust various development and production settings by setting environment variables in your shell or with [.env](#adding-development-environment-variables-in-env).

Variable | Development | Production | Usage
:--- | :---: | :---: | :---
BROWSER | :white_check_mark: | :x: | By default, Create React App will open the default system browser, favoring Chrome on macOS. Specify a [browser](https://github.com/sindresorhus/opn#app) to override this behavior, or set it to `none` to disable it completely.
HOST | :white_check_mark: | :x: | By default, the development web server binds to `localhost`. You may use this variable to specify a different host.
PORT | :white_check_mark: | :x: | By default, the development web server will attempt to listen on port 3000 or prompt you to attempt the next available port. You may use this variable to specify a different port.
HTTPS | :white_check_mark: | :x: | When set to `true`, Create React App will run the development server in `https` mode.
PUBLIC_URL | :x: | :white_check_mark: | Create React App assumes your application is hosted at the serving web server's root or a subpath as specified in [`package.json` (`homepage`)](#building-for-relative-paths). Normally, Create React App ignores the hostname. You may use this variable to force assets to be referenced verbatim to the url you provide (hostname included). This may be particularly useful when using a CDN to host your application.
CI | :large_orange_diamond: | :white_check_mark: | When set to `true`, Create React App treats warnings as failures in the build. It also makes the test runner non-watching. Most CIs set this flag by default.

## Troubleshooting

### `npm start` doesn’t detect changes

When you save a file while `npm start` is running, the browser should refresh with the updated code.<br>
If this doesn’t happen, try one of the following workarounds:

* If your project is in a Dropbox folder, try moving it out.
* If the watcher doesn’t see a file called `index.js` and you’re referencing it by the folder name, you [need to restart the watcher](https://github.com/facebookincubator/create-react-app/issues/1164) due to a Webpack bug.
* Some editors like Vim and IntelliJ have a “safe write” feature that currently breaks the watcher. You will need to disable it. Follow the instructions in [“Working with editors supporting safe write”](https://webpack.github.io/docs/webpack-dev-server.html#working-with-editors-ides-supporting-safe-write).
* If your project path contains parentheses, try moving the project to a path without them. This is caused by a [Webpack watcher bug](https://github.com/webpack/watchpack/issues/42).
* On Linux and macOS, you might need to [tweak system settings](https://webpack.github.io/docs/troubleshooting.html#not-enough-watchers) to allow more watchers.
* If the project runs inside a virtual machine such as (a Vagrant provisioned) VirtualBox, create an `.env` file in your project directory if it doesn’t exist, and add `CHOKIDAR_USEPOLLING=true` to it. This ensures that the next time you run `npm start`, the watcher uses the polling mode, as necessary inside a VM.

If none of these solutions help please leave a comment [in this thread](https://github.com/facebookincubator/create-react-app/issues/659).

### `npm test` hangs on macOS Sierra

If you run `npm test` and the console gets stuck after printing `react-scripts test --env=jsdom` to the console there might be a problem with your [Watchman](https://facebook.github.io/watchman/) installation as described in [facebookincubator/create-react-app#713](https://github.com/facebookincubator/create-react-app/issues/713).

We recommend deleting `node_modules` in your project and running `npm install` (or `yarn` if you use it) first. If it doesn't help, you can try one of the numerous workarounds mentioned in these issues:

* [facebook/jest#1767](https://github.com/facebook/jest/issues/1767)
* [facebook/watchman#358](https://github.com/facebook/watchman/issues/358)
* [ember-cli/ember-cli#6259](https://github.com/ember-cli/ember-cli/issues/6259)

It is reported that installing Watchman 4.7.0 or newer fixes the issue. If you use [Homebrew](http://brew.sh/), you can run these commands to update it:

```
watchman shutdown-server
brew update
brew reinstall watchman
```

You can find [other installation methods](https://facebook.github.io/watchman/docs/install.html#build-install) on the Watchman documentation page.

If this still doesn’t help, try running `launchctl unload -F ~/Library/LaunchAgents/com.github.facebook.watchman.plist`.

There are also reports that *uninstalling* Watchman fixes the issue. So if nothing else helps, remove it from your system and try again.

### `npm run build` silently fails

It is reported that `npm run build` can fail on machines with no swap space, which is common in cloud environments. If [the symptoms are matching](https://github.com/facebookincubator/create-react-app/issues/1133#issuecomment-264612171), consider adding some swap space to the machine you’re building on, or build the project locally.

### `npm run build` fails on Heroku

This may be a problem with case sensitive filenames.
Please refer to [this section](#resolving-heroku-deployment-errors).

## Something Missing?

If you have ideas for more “How To” recipes that should be on this page, [let us know](https://github.com/facebookincubator/create-react-app/issues) or [contribute some!](https://github.com/facebookincubator/create-react-app/edit/master/packages/react-scripts/template/README.md)