README.md

1. If possible, configure your production environment to serve the generated
`service-worker.js` [with HTTP caching disabled](http://stackoverflow.com/questions/38843970/service-worker-javascript-update-frequency-every-24-hours).
If that's not possible—[GitHub Pages](#github-pages), for instance, does not
allow you to change the default 10 minute HTTP cache lifetime—then be aware
that if you visit your production site, and then revisit again before
`service-worker.js` has expired from your HTTP cache, you'll continue to get
the previously cached assets from the service worker. If you have an immediate
need to view your updated production deployment, performing a shift-refresh
will temporarily disable the service worker and retrieve all assets from the
network.

1. Users aren't always familiar with offline-first web apps. It can be useful to
[let the user know](https://developers.google.com/web/fundamentals/instant-and-offline/offline-ux#inform_the_user_when_the_app_is_ready_for_offline_consumption)
when the service worker has finished populating your caches (showing a "This web
app works offline!" message) and also let them know when the service worker has
fetched the latest updates that will be available the next time they load the
page (showing a "New content is available; please refresh." message). Showing
this messages is currently left as an exercise to the developer, but as a
starting point, you can make use of the logic included in [`src/registerServiceWorker.js`](src/registerServiceWorker.js), which
demonstrates which service worker lifecycle events to listen for to detect each
scenario, and which as a default, just logs appropriate messages to the
JavaScript console.

1. By default, the generated service worker file will not intercept or cache any
cross-origin traffic, like HTTP [API requests](#integrating-with-an-api-backend),
images, or embeds loaded from a different domain. If you would like to use a
runtime caching strategy for those requests, you can [`eject`](#npm-run-eject)
and then configure the
[`runtimeCaching`](https://github.com/GoogleChrome/sw-precache#runtimecaching-arrayobject)
option in the `SWPrecacheWebpackPlugin` section of
[`webpack.config.prod.js`](../config/webpack.config.prod.js).

### Progressive Web App Metadata

The default configuration includes a web app manifest located at
[`public/manifest.json`](public/manifest.json), that you can customize with
details specific to your web application.

When a user adds a web app to their homescreen using Chrome or Firefox on
Android, the metadata in [`manifest.json`](public/manifest.json) determines what
icons, names, and branding colors to use when the web app is displayed.
[The Web App Manifest guide](https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/)
provides more context about what each field means, and how your customizations
will affect your users' experience.

## Analyzing the Bundle Size

[Source map explorer](https://www.npmjs.com/package/source-map-explorer) analyzes
JavaScript bundles using the source maps. This helps you understand where code
bloat is coming from.

To add Source map explorer to a Create React App project, follow these steps:

```sh
npm install --save source-map-explorer
```

Alternatively you may use `yarn`:

```sh
yarn add source-map-explorer
```

Then in `package.json`, add the following line to `scripts`:

```diff
   "scripts": {
+    "analyze": "source-map-explorer build/static/js/main.*",
     "start": "react-scripts start",
     "build": "react-scripts build",
     "test": "react-scripts test --env=jsdom",
```

Then to analyze the bundle run the production build then run the analyze
script.

```
npm run build
npm run analyze
```

## Deployment

`npm run build` creates a `build` directory with a production build of your app. Set up your favorite 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.

### Static Server

For environments using [Node](https://nodejs.org/), the easiest way to handle this would be to install [serve](https://github.com/zeit/serve) and let it handle the rest:

```sh
npm install -g serve
serve -s build
```

The last command shown above will serve your static site on the port **5000**. Like many of [serve](https://github.com/zeit/serve)’s internal settings, the port can be adjusted using the `-p` or `--port` flags.

Run this command to get a full list of the options available:

```sh
serve -h
```

### Other Solutions

You don’t necessarily need a static server in order to run a Create React App project in production. It works just as fine integrated into an existing dynamic one.

Here’s a programmatic example using [Node](https://nodejs.org/) and [Express](http://expressjs.com/):

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

app.use(express.static(path.join(__dirname, 'build')));

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

app.listen(9000);
```

The choice of your server software isn’t important either. Since Create React App is completely platform-agnostic, there’s no need to explicitly use Node.

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(path.join(__dirname, 'build')));

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

If you’re using [Apache HTTP Server](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`.

If you’re using [Apache Tomcat](http://tomcat.apache.org/), you need to follow [this Stack Overflow answer](https://stackoverflow.com/a/41249464/4878474).

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

When users install your app to the homescreen of their device the default configuration will make a shortcut to `/`. This may not work if you don't use a client-side router and expect the app to be served from `/index.html`. In this case, the web app manifest at [`public/manifest.json`](public/manifest.json) and change `start_url` to `./index.html`.

### Service Worker Considerations

[Navigation requests](https://developers.google.com/web/fundamentals/primers/service-workers/high-performance-loading#first_what_are_navigation_requests)
for URLs like `/todos/42` will not be intercepted by the
[service worker](https://developers.google.com/web/fundamentals/getting-started/primers/service-workers)
created by the production build. Navigations for those URLs will always
require a network connection, as opposed to navigations for `/` and
`/index.html`, both of which will be served from the cache by the service worker
and work without requiring a network connection.

If you are using the `pushState` history API and would like to enable service
worker support for navigations to URLs like `/todos/42`, you need to
[`npm eject`](#npm-run-eject) and enable the [`navigateFallback`](https://github.com/GoogleChrome/sw-precache#navigatefallback-string)
and [`navigateFallbackWhitelist`](https://github.com/GoogleChrome/sw-precache#navigatefallbackwhitelist-arrayregexp)
options of the `SWPreachePlugin` [configuration](../config/webpack.config.prod.js).

>Note: This is a [change in default behavior](https://github.com/facebook/create-react-app/issues/3248),
as earlier versions of `create-react-app` shipping with `navigateFallback`
enabled by default.

### 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.

**Note**: If you are using `react-router@^4`, you can root `<Link>`s using the `basename` prop on any `<Router>`.<br>
More information [here](https://reacttraining.com/react-router/web/api/BrowserRouter/basename-string).<br>
<br>
For example:
```js
<BrowserRouter basename="/calendar"/>
<Link to="/today"/> // renders <a href="/calendar/today">
```

#### 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](https://azure.microsoft.com/)

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.

See [this](https://medium.com/@strid/host-create-react-app-on-azure-986bc40d5bf2#.pycfnafbg) blog post or [this](https://github.com/ulrikaugustsson/azure-appservice-static) repo for a way to use automatic deployment to Azure App Service.

### [Firebase](https://firebase.google.com/)

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!
```

IMPORTANT: you need to set proper HTTP caching headers for `service-worker.js` file in `firebase.json` file or you will not be able to see changes after first deployment ([issue #2440](https://github.com/facebook/create-react-app/issues/2440)). It should be added inside `"hosting"` key like next:

```
{
  "hosting": {
    ...
    "headers": [
      {"source": "/service-worker.js", "headers": [{"key": "Cache-Control", "value": "no-cache"}]}
    ]
    ...
```

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](https://pages.github.com/)

>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 for your project:

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

or for a GitHub user page:

```json
  "homepage": "https://myusername.github.io",
```

or for a custom domain page:
```json
  "homepage": "https://mywebsite.com",
```

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 gh-pages
```

Alternatively you may use `yarn`:

```sh
yarn add gh-pages
```

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

```diff
  "scripts": {
+   "predeploy": "npm run build",
+   "deploy": "gh-pages -d build",
    "start": "react-scripts start",
    "build": "react-scripts build",
```

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

If you are deploying to a GitHub user page instead of a project page you'll need to make two
additional modifications:

1. First, change your repository's source branch to be any branch other than **master**.
1. Additionally, tweak your `package.json` scripts to push deployments to **master**:
```diff
  "scripts": {
    "predeploy": "npm run build",
-   "deploy": "gh-pages -d build",
+   "deploy": "gh-pages -b master -d build",
```

#### 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.

Your CNAME file should look like this:

```
mywebsite.com
```

#### 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://reacttraining.com/react-router/web/api/Router) 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).

#### Troubleshooting

##### "/dev/tty: No such a device or address"

If, when deploying, you get `/dev/tty: No such a device or address` or a similar error, try the follwing:

1. Create a new [Personal Access Token](https://github.com/settings/tokens)
2. `git remote set-url origin https://<user>:<token>@github.com/<user>/<repo>` .
3. Try `npm run deploy again`

### [Heroku](https://www.heroku.com/)

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`.

### [Netlify](https://www.netlify.com/)

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

```sh
npm install netlify-cli -g
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](https://zeit.co/now)

Now offers a zero-configuration single-command deployment. You can use `now` to deploy your app for free.

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. Build your app by running `npm run build`.

3. Move into the build directory by running `cd build`.

4. Run `now --name your-project-name` from within the build directory. You will see a **now.sh** URL in your output like this:

    ```
    > Ready! https://your-project-name-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/unlimited-static)

### [S3](https://aws.amazon.com/s3) and [CloudFront](https://aws.amazon.com/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 and CloudFront.

### [Surge](https://surge.sh/)

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.

When asked about the project path, make sure to specify the `build` folder, for example:

```sh
       project path: /path/to/project/build
```

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. If you need to customize the way the browser is launched, you can specify a node script instead. Any arguments passed to `npm start` will also be passed to this script, and the url where your app is served will be the last argument. Your script's file name must have the `.js` extension.
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.
REACT_EDITOR | :white_check_mark: | :x: | When an app crashes in development, you will see an error overlay with clickable stack trace. When you click on it, Create React App will try to determine the editor you are using based on currently running processes, and open the relevant source file. You can [send a pull request to detect your editor of choice](https://github.com/facebook/create-react-app/issues/2636). Setting this environment variable overrides the automatic detection. If you do it, make sure your systems [PATH](https://en.wikipedia.org/wiki/PATH_(variable)) environment variable points to your editor’s bin folder. You can also set it to `none` to disable it completely.
CHOKIDAR_USEPOLLING | :white_check_mark: | :x: | When set to `true`, the watcher runs in polling mode, as necessary inside a VM. Use this option if `npm start` isn't detecting changes.
GENERATE_SOURCEMAP | :x: | :white_check_mark: | When set to `false`, source maps are not generated for a production build. This solves OOM issues on some smaller machines.
NODE_PATH | :white_check_mark: |  :white_check_mark: | Same as [`NODE_PATH` in Node.js](https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders), but only relative folders are allowed. Can be handy for emulating a monorepo setup by setting `NODE_PATH=src`.

## 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/facebook/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 [“Adjusting Your Text Editor”](https://webpack.js.org/guides/development/#adjusting-your-text-editor).
* 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://github.com/webpack/docs/wiki/troubleshooting#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/facebook/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 [facebook/create-react-app#713](https://github.com/facebook/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` exits too early

It is reported that `npm run build` can fail on machines with limited memory and no swap space, which is common in cloud environments. Even with small projects this command can increase RAM usage in your system by hundreds of megabytes, so if you have less than 1 GB of available memory your build is likely to fail with the following message:

>  The build failed because the process exited too early. This probably means the system ran out of memory or someone called `kill -9` on the process.

If you are completely sure that you didn't terminate the process, consider [adding some swap space](https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04) 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).

### Moment.js locales are missing

If you use a [Moment.js](https://momentjs.com/), you might notice that only the English locale is available by default. This is because the locale files are large, and you probably only need a subset of [all the locales provided by Moment.js](https://momentjs.com/#multiple-locale-support).

To add a specific Moment.js locale to your bundle, you need to import it explicitly.<br>
For example:

```js
import moment from 'moment';
import 'moment/locale/fr';
```

If import multiple locales this way, you can later switch between them by calling `moment.locale()` with the locale name:

```js
import moment from 'moment';
import 'moment/locale/fr';
import 'moment/locale/es';

// ...

moment.locale('fr');
```

This will only work for locales that have been explicitly imported before.

### `npm run build` fails to minify

Some third-party packages don't compile their code to ES5 before publishing to npm. This often causes problems in the ecosystem because neither browsers (except for most modern versions) nor some tools currently support all ES6 features. We recommend to publish code on npm as ES5 at least for a few more years.

<br>
To resolve this:

1. Open an issue on the dependency's issue tracker and ask that the package be published pre-compiled.
  * Note: Create React App can consume both CommonJS and ES modules. For Node.js compatibility, it is recommended that the main entry point is CommonJS. However, they can optionally provide an ES module entry point with the `module` field in `package.json`. Note that **even if a library provides an ES Modules version, it should still precompile other ES6 features to ES5 if it intends to support older browsers**.

2. Fork the package and publish a corrected version yourself.

3. If the dependency is small enough, copy it to your `src/` folder and treat it as application code.

In the future, we might start automatically compiling incompatible third-party modules, but it is not currently supported. This approach would also slow down the production builds.

## Alternatives to Ejecting

[Ejecting](#npm-run-eject) lets you customize anything, but from that point on you have to maintain the configuration and scripts yourself. This can be daunting if you have many similar projects. In such cases instead of ejecting we recommend to *fork* `react-scripts` and any other packages you need. [This article](https://auth0.com/blog/how-to-configure-create-react-app/) dives into how to do it in depth. You can find more discussion in [this issue](https://github.com/facebook/create-react-app/issues/682).

## Something Missing?

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