README
Last updated
Was this helpful?
Last updated
Was this helpful?
This example is forked from
This project was bootstrapped with .
Below you will find some information on how to perform common tasks. You can find the most recent version of this guide .
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.
We commit to keeping the breaking changes minimal so you can upgrade react-scripts painlessly.
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.
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.
In the project directory, you can run:
npm startThe page will reload if you make edits. You will also see any lint errors in the console.
npm testnpm run buildBuilds 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 ejectNote: 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.
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.
Note: this feature is available with
react-scripts@0.2.0and higher. 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:
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.
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.
Then add the block below to your launch.json file and put it inside the .vscode folder in your app’s root directory.
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.
<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.
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:
For example:
Button.jsDangerButton.jsWe 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:
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.
Here is an example:
moduleA.jsApp.jsThis 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.
Button.cssButton.jsIn 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.
For example, this:
becomes this:
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:
Then in package.json, add the following lines to scripts:
Note: To use a different preprocessor, replace
build-cssandwatch-csscommands 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.
This will allow you to do imports like
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:
Then we can change start and build scripts to include the CSS preprocessor commands:
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.
node-sass-chokidar is used here as it addresses these issues.
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.
Here is an example:
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:
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.
public FolderNote: this feature is available with
react-scripts@0.5.0and higher.
You can also add other assets to the public folder.
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:
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:
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.
public FolderYou have thousands of images and need to dynamically reference their paths.
Some library may be incompatible with Webpack and you have no other option but to include it as a <script> tag.
Note that if you add a <script> that declares global variables, you also need to read the next section on using them.
When you include a script in the HTML file that defines global variables and try to use one of these variables in the code, the linter will complain because it cannot see the definition of the variable.
You can avoid this by reading the global variable explicitly from the window object, for example:
This makes it obvious you are using a global variable intentionally rather than because of a typo.
Alternatively, you can force the linter to ignore any line by adding // eslint-disable-line after it.
Install React Bootstrap and Bootstrap from npm. React Bootstrap does not include Bootstrap CSS so this needs to be installed as well:
Import Bootstrap CSS and optionally Bootstrap theme CSS in the beginning of your src/index.js file:
Import required React Bootstrap components within src/App.js file or your custom component files:
Sometimes you might need to tweak the visual styles of Bootstrap (or equivalent package). We suggest the following approach:
Create a new package that depends on the package you wish to customize, e.g. Bootstrap.
Add the necessary build steps to tweak the theme, and publish your package on npm.
Install your own theme npm package as a dependency of your app.
To add Flow to a Create React App project, follow these steps:
Run npm install --save-dev flow-bin (or yarn add --dev flow-bin).
Add "flow": "flow" to the scripts section of your package.json.
Add // @flow to any files you want to type check (for example, to src/App.js).
Note: this feature is available with
react-scripts@0.2.3and higher.
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.
There is also a special built-in environment variable called NODE_ENV. You can read it from process.env.NODE_ENV. When you run npm start, it is always equal to 'development', when you run npm test it is always equal to 'test', and when you run npm run build to make a production bundle, it is always equal to 'production'. You cannot override NODE_ENV manually. This prevents developers from accidentally deploying a slow development build to production.
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>:
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:
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. Both of these ways are described in the next few sections.
Having access to the NODE_ENV is also useful for performing actions conditionally:
When you compile the app with npm run build, the minification step will strip out this condition, and the resulting bundle will be smaller.
Note: this feature is available with
react-scripts@0.9.0and higher.
You can also access the environment variables starting with REACT_APP_ in the public/index.html. For example:
Note that the caveats from the above section apply:
Apart from a few built-in variables (NODE_ENV and PUBLIC_URL), variable names must start with REACT_APP_ to work.
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)
(Note: the lack of whitespace is intentional.)
Linux, macOS (Bash)
.envNote: this feature is available with
react-scripts@0.5.0and higher.
To define permanent environment variables, create a file called .env in the root of your project:
.env files should be checked into source control (with the exclusion of .env*.local).
What other .env files are can be used?
Note: this feature is available with
react-scripts@1.0.0and higher.
.env: Default.
.env.local: Local overrides. This file is loaded for all environments except test.
.env.development, .env.test, .env.production: Environment-specific settings.
.env.development.local, .env.test.local, .env.production.local: Local overrides of environment-specific settings.
Files on the left have more priority than files on the right:
npm start: .env.development.local, .env.development, .env.local, .env
npm run build: .env.production.local, .env.production, .env.local, .env
npm test: .env.test.local, .env.test, .env (note .env.local is missing)
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:
Create React App will add decorator support when the specification advances to a stable stage.
These tutorials will help you to integrate your app with an API backend running on another port, using fetch() to access it.
Note: this feature is available with
react-scripts@0.2.3and higher.
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:
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:
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.
Keep in mind that proxy only has effect in development (with npm start), and it is up to you to ensure that URLs like /api/todos point to the right thing in production. You don’t have to use the /api prefix. Any unrecognized request without a text/html accept header will be redirected to the specified proxy.
The proxy option supports HTTP, HTTPS and WebSocket connections.
If the proxy option is not flexible enough for you, alternatively you can:
Invalid Host header
To work around it, you can specify your public development host in a file called .env.development in the root of your project:
If you restart the development server now and load the app from the specified host, it should work.
If you are still having issues or if you’re using a more exotic environment like a cloud editor, you can bypass the host check completely by adding a line to .env.development.local. Note that this is dangerous and exposes your machine to remote code execution from malicious websites:
We don’t recommend this approach.
Note: this feature is available with
react-scripts@1.0.0and higher.
All requests matching this path will be proxies, no exceptions. This includes requests for text/html, which the standard proxy option does not proxy.
If you need to specify multiple proxies, you may do so by specifying additional entries. You may also narrow down matches using * and/or **, to match the path exactly or any subpath.
Note: this feature is available with
react-scripts@0.4.0and higher.
To do this, set the HTTPS environment variable to true, then start the dev server as usual with npm start:
Windows (cmd.exe)
(Note: the lack of whitespace is intentional.)
Linux, macOS (Bash)
Note that the server will use a self-signed certificate, so your web browser will almost definitely display a warning upon accessing the page.
<meta> Tags on the ServerSince Create React App doesn’t support server rendering, you might be wondering how to make <meta> tags dynamic and reflect the current URL. To solve this, we recommend to add placeholders into the HTML, like this:
Then, on the server, regardless of the backend you use, you can read index.html into memory and replace __OG_TITLE__, __OG_DESCRIPTION__, and any other placeholders with values depending on the current URL. Just make sure to sanitize and escape the interpolated values so that they are safe to embed into HTML!
If you use a Node server, you can even share the route matching logic between the client and the server. However duplicating it also works fine in simple cases.
There are also opportunities to use this outside of static hosting, to take the pressure off the server when generating and caching routes.
The primary benefit of pre-rendering is that you get the core content of each page with the HTML payload—regardless of whether or not your JavaScript bundle successfully downloads. It also increases the likelihood that each route of your application will be picked up by search engines.
Similarly to the previous section, you can leave some placeholders in the HTML that inject global variables, for example:
Jest is a Node-based runner. This means that the tests always run in a Node environment and not in a real browser. This lets us enable fast iteration speed and prevent flakiness.
We recommend that you use a separate tool for browser end-to-end tests if you need them. They are beyond the scope of Create React App.
Jest will look for test files with any of the following popular naming conventions:
Files with .js suffix in __tests__ folders.
Files with .test.js suffix.
Files with .spec.js suffix.
The .test.js / .spec.js files (or the __tests__ folders) can be located at any depth under the src top level folder.
We recommend to put the test files (or __tests__ folders) next to the code they are testing so that relative imports appear shorter. For example, if App.test.js and App.js are in the same folder, the test just needs to import App from './App' instead of a long relative path. Colocation also helps find tests more quickly in larger projects.
When you run npm test, Jest will launch in the watch mode. Every time you save a file, it will re-run the tests, just like npm start recompiles the code.
The watcher includes an interactive command-line interface with the ability to run all tests, or focus on a search pattern. It is designed this way so that you can keep it open and enjoy fast re-runs. You can learn the commands from the “Watch Usage” note that the watcher prints after every run:
By default, when you run npm test, Jest will only run the tests related to files changed since the last commit. This is an optimization designed to make your tests runs fast regardless of how many tests you have. However it assumes that you don’t often commit the code that doesn’t pass the tests.
Jest will always explicitly mention that it only ran tests related to the files changed since the last commit. You can also press a in the watch mode to force Jest to run all tests.
To create tests, add it() (or test()) blocks with the name of the test and its code. You may optionally wrap them in describe() blocks for logical grouping but this is neither required nor recommended.
Jest provides a built-in expect() global function for making assertions. A basic test could look like this:
There is a broad spectrum of component testing techniques. They range from a “smoke test” verifying that a component renders without throwing, to shallow rendering and testing some of the output, to full rendering and testing component lifecycle and state changes.
Different projects choose different testing tradeoffs based on how often components change, and how much logic they contain. If you haven’t decided on a testing strategy yet, we recommend that you start with creating simple smoke tests for your components:
This test mounts a component and makes sure that it didn’t throw during rendering. Tests like this provide a lot value with very little effort so they are great as a starting point, and this is the test you will find in src/App.test.js.
When you encounter bugs caused by changing components, you will gain a deeper insight into which parts of them are worth testing in your application. This might be a good time to introduce more specific tests asserting specific expected output or behavior.
Here is an example from Enzyme documentation that asserts specific output, rewritten to use Jest matchers:
and then use them in your tests like you normally do.
Note: this feature is available with
react-scripts@0.4.0and 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
You can replace it() with xit() to temporarily exclude a test from being executed.
Similarly, fit() lets you focus on a specific test without running any other tests.
Jest has an integrated coverage reporter that works well with ES6 and requires no configuration.
Run npm test -- --coverage (note extra -- in the middle) to include a coverage report like this:
Note that tests run much slower with coverage so it is recommended to run it separately from your normal workflow.
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:
Travis CI
Add a .travis.yml file to your git repository.
Trigger your first build with a git push.
Windows (cmd.exe)
(Note: the lack of whitespace is intentional.)
Linux, macOS (Bash)
The test command will force Jest to run tests once instead of launching the watcher.
The build command will check for linter warnings and fail if any are found.
By default, the package.json of the generated project looks like this:
Any browser globals like window and document
In contrast, jsdom is not needed for the following APIs:
Progressive Web Apps are faster and more reliable than traditional web pages, and provide an engaging mobile experience:
All static site assets are cached so that your page loads fast on subsequent visits, regardless of network connectivity (such as 2G or 3G). Updates are downloaded in the background.
Your app will work regardless of network state, even if offline. This means your users will be able to use your app at 10,000 feet and on the Subway.
On mobile devices, your app can be added directly to the user's home screen, app icon and all. You can also re-engage users using web push notifications. This eliminates the need for the app store.
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.
Run this command to get a full list of the options available:
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.
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.
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:
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.
By default, Create React App produces a build assuming your app is hosted at the server root.
To override this, specify the homepage in your package.json, for example:
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@0.9.0and 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:
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.
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.
Now, after you create a production build with npm run build, you can deploy it by running firebase deploy.
Note: this feature is available with
react-scripts@0.2.0and higher.
Step 1: Add homepage to package.json
The step below is important! If you skip it, your app will not deploy correctly.
Open your package.json and add a homepage field:
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.
Add the following scripts in your package.json:
The predeploy script will run automatically before deploy is run.
Step 3: Deploy the site by running npm run deploy
Then run:
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:
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:
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:
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:
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.
To do a manual deploy to Netlify’s CDN:
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:
Pick your Git hosting service and select your repository
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:
When you build the project, Create React App will place the public folder contents into the build output.
Build your app by running npm run build.
Move into the build directory by running cd build.
Run now --name your-project-name from within the build directory. You will see a now.sh URL in your output like this:
Paste that URL into your browser when the build is complete, and you will see your deployed app.
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:
Variable
Development
Production
Usage
BROWSER
:white_check_mark:
:x:
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:
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.
npm start doesn’t detect changesWhen you save a file while npm start is running, the browser should refresh with the updated code.
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 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.
npm test hangs on macOS SierraWe 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:
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 failsnpm run build fails on HerokuTo add a specific Moment.js locale to your bundle, you need to import it explicitly. For example:
If import multiple locales this way, you can later switch between them by calling moment.locale() with the locale name:
This will only work for locales that have been explicitly imported before.
To update an existing project to a new version of react-scripts, , 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 for potential breaking changes.
We are always open to .
Runs the app in the development mode. Open to view it in the browser.
Launches the test runner in the interactive watch mode. See the section about for more information.
See the section about for more information.
This project supports a superset of the latest JavaScript standard. In addition to syntax features, it also supports:
(ES2016).
(ES2017).
(stage 3 proposal).
(stage 3 proposal)
(stage 2 proposal).
and syntax.
Learn more about .
While we recommend to use experimental proposals with some caution, Facebook heavily uses these features in the product code, so we intend to provide if any of these proposals change in the future.
Note that the project only includes a few ES6 :
via .
via .
via .
To configure the syntax highlighting in your favorite text editor, head to the and follow the instructions. Some of the most popular editors are covered.
If you want to enforce a coding style for your project, consider using instead of ESLint style rules.
This feature is currently only supported by editor.
You would need to have the latest version of and VS Code installed.
Note that normally you wouldn’t edit files in the public folder very often. For example, is done without touching the HTML.
If you need to dynamically update the page title based on the content, you can use the browser API. For more complex scenarios when you want to change the title from React components, you can use , 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 . Alternatively, you can pre-build each page as a static HTML file which then loads the JavaScript bundle, which is covered .
This project setup supports ES6 modules thanks to Babel.
While you can still use require() and module.exports, we encourage you to use instead.
Be aware of the . It is a common source of mistakes.
This project setup supports code splitting via . Its is in stage 3. The import() function-like form takes the module name as an argument and returns a which always resolves to the namespace object of the module.
This project setup uses 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:
This is not required for React but many people find this feature convenient. You can read about the benefits of this approach . However you should be aware that this makes your code less portable to other build tools and environments than Webpack.
This project setup minifies your CSS and adds vendor prefixes to it automatically through so you don’t need to worry about it.
If you need to disable autoprefixing for some reason, .
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 ).
Infinite styles compiling
node-sass has been reported as having issues with detecting new files in a directory
To reduce the number of requests to the server, importing images that are less than 10,000 bytes returns a instead of a path. This applies to the following file extensions: bmp, gif, jpg, jpeg, and png. SVG files are excluded due to .
The public folder contains the HTML file so you can tweak it, for example, to . The <script> tag with the compiled code will be added to it automatically during the build process.
Note that we normally encourage you to import assets in JavaScript files instead. For example, see the sections on and . This mechanism provides a number of benefits:
Normally we recommend importing , from JavaScript. The public folder is useful as a workaround for a number of less common cases:
You need a file with a specific name in the build output, such as .
You want to include a small script like outside of the bundled code.
You don’t have to use 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:
Now you are ready to use the imported React Bootstrap components within your component hierarchy defined in the render method. Here is an example redone using React Bootstrap.
Here is an example of adding a that follows these steps.
Flow is a static type checker that helps you write code with fewer bugs. Check out this if you are new to this concept.
Recent versions of work with Create React App projects out of the box.
Run npm run flow -- init (or yarn flow -- init) to create a in the root directory.
Now you can run npm run flow (or yarn flow) to check the files for type errors. You can optionally use an IDE like for a better integrated experience. In the future we plan to integrate it into Create React App even more closely.
To learn more about Flow, check out .
The environment variables are embedded during the build time. Since Create React App produces a static HTML/CSS/JS bundle, it can’t possibly read them at runtime. To read them at runtime, you would need to load HTML into memory on the server and replace placeholders in runtime, just like . Alternatively you can rebuild the app on the server anytime you change them.
Note: You must create custom environment variables beginning with REACT_APP_. Any other variables except NODE_ENV will be ignored to avoid accidentally . Changing any environment variables will require you to restart the development server if it is running.
The environment variables are injected at build time. If you need to inject them at runtime, .
These variables will act as the defaults if the machine does not explicitly set them. Please refer to the for more details.
Note: If you are defining environment variables for development, your CI and/or hosting platform will most likely need these defined as well. Consult their documentation how to do this. For example, see the documentation for or .
Many popular libraries use in their documentation. Create React App doesn’t support decorator syntax at the moment because:
Check out . You can find the companion GitHub repository .
Check out . You can find the companion GitHub repository .
Conveniently, this avoids and error messages like this in development:
Enable CORS on your server ().
Use to inject the right server host and port into your app.
When you enable the proxy option, you opt into a more strict set of host checks. This is necessary because leaving the backend open to remote hosts makes your computer vulnerable to DNS rebinding attacks. The issue is explained in and .
This shouldn’t affect you when developing on localhost, but if you develop remotely like , you will see this error in the browser after enabling the proxy option:
If the proxy option is not flexible enough for you, you can specify an object in the following form (in package.json).
You may also specify any configuration value or supports.
You may require the dev server to serve pages over HTTPS. One particular case where this could be useful is when using to proxy requests to an API server when that API server is itself serving HTTPS.
If you’re hosting your build with a static hosting provider you can use to generate HTML pages for each route, or relative link, in your application. These pages will then seamlessly become active, or “hydrated”, when the JavaScript bundle has loaded.
You can read more about .
Then, on the server, you can replace __SERVER_DATA__ with a JSON of real data right before sending the response. The client code can then read window.SERVER_DATA to use it. Make sure to as it makes your app vulnerable to XSS attacks.
Note: this feature is available with react-scripts@0.3.0 and higher.
Create React App uses as its test runner. To prepare for this integration, we did a of Jest so if you heard bad things about it years ago, give it another try.
While Jest provides browser globals such as window thanks to , they are only approximations of the real browser behavior. Jest is intended to be used for unit tests of your logic and your components rather than the DOM quirks.
Jest will always run all tests on a server or if the project is not inside a Git or Mercurial repository.
All expect() matchers supported by Jest are .
You can also use to create “spies” or mock functions.
If you’d like to test components in isolation from the child components they render, we recommend using from . You can write a smoke test with it too:
Unlike the previous smoke test using ReactDOM.render(), this test only renders <App> and doesn’t go deeper. For example, even if <App> itself renders a <Button> that throws, this test will pass. Shallow rendering is great for isolated unit tests, but you may still want to create some full rendering tests to ensure the components integrate correctly. Enzyme supports , and you can also use it for testing state changes and component lifecycle.
You can read the for more testing techniques. Enzyme documentation uses Chai and Sinon for assertions but you don’t have to use them because Jest provides built-in expect() and jest.fn() for spies.
All Jest matchers are . Nevertheless you can use a third-party assertion library like if you want to, as described below.
Additionally, you might find helpful to simplify your tests with readable matchers. The above contains code can be written simpler with jest-enzyme.
To setup jest-enzyme with Create React App, follow the instructions for to import jest-enzyme. Note that currently only version 2.x is compatible with Create React App.
We recommend that you use expect() for assertions and jest.fn() for spies. If you are having issues with them please , and we’ll fix them. We intend to keep making them better for React, supporting, for example, .
However, if you are used to other libraries, such as and , or if you have existing code using them that you’d like to port over, you can import them normally like this:
Following the guide for syncing your GitHub repository with Travis. You may need to initialize some settings manually in your page.
if needed.
If you find yourself doing this often in development, please 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.
If you know that none of your tests depend on , you can safely remove --env=jsdom, and your tests will run faster.
To help you make up your mind, here is a list of APIs that need jsdom:
( for the above)
in
(shallow rendering)
in
Finally, jsdom is also not needed for .
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.
If you use , there is a 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.
By default, the production build is a fully functional, offline-first .
The is integrated into production configuration, and it will take care of generating a service worker file that will automatically precache all of your local assets and keep them up to date as you deploy updates. The service worker will use a for handling all requests for local assets, including the initial HTML, ensuring that you web app is reliably fast, even on a slow or unreliable network.
If you would prefer not to enable service workers prior to your initial production deployment, then remove the call to serviceWorkerRegistration.register() from .
If you had previously enabled service workers in your production deployment and have decided that you would like to disable them for all your existing users, you can swap out the call to serviceWorkerRegistration.register() in with a call to serviceWorkerRegistration.unregister(). After the user visits a page that has serviceWorkerRegistration.unregister(), the service worker will be uninstalled.
Service workers , although to facilitate local testing, that policy . If your production web server does not support HTTPS, then the service worker registration will fail, but the rest of your web app will remain functional.
Service workers are in all web browsers. Service worker registration on browsers that lack support.
The service worker is only enabled in the , e.g. the output of npm run build. It's recommended that you do not enable an offline-first service worker in a development environment, as it can lead to frustration when previously cached assets are used and do not include the latest changes you've made locally.
If you need to test your offline-first service worker locally, build the application (using npm run build) and run a simple http server from your build directory. After running the build script, create-react-app will give instructions for one way to test your production build locally and the have instructions for using other methods. Be sure to always use an incognito window to avoid complications with your browser cache.
If possible, configure your production environment to serve the generated service-worker.js . If that's not possible—, 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.
Users aren't always familiar with offline-first web apps. It can be useful to 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 , 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.
By default, the generated service worker file will not intercept or cache any cross-origin traffic, like HTTP , images, or embeds loaded from a different domain. If you would like to use a runtime caching strategy for those requests, you can and then configure the option in the SWPrecacheWebpackPlugin section of .
The default configuration includes a web app manifest located at , 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 determines what icons, names, and branding colors to use when the web app is displayed. provides more context about what each field means, and how your customizations will affect your users' experience.
For environments using , the easiest way to handle this would be to install and let it handle the rest:
The last command shown above will serve your static site on the port 5000. Like many of ’s internal settings, the port can be adjusted using the -p or --port flags.
Here’s a programmatic example using and :
If you use routers that use the HTML5 under the hood (for example, 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.
If you’re using , you need to create a .htaccess file in the public folder that looks like this:
On a production build, and in a browser that supports , the service worker will automatically handle all navigation requests, like for /todos/42, by serving the cached copy of your index.html. This service worker navigation routing can be configured or disabled by and then modifying the and options of the SWPreachePlugin .
See blog post on how to deploy your React app to .
Install the Firebase CLI if you haven’t already by running npm install -g firebase-tools. Sign up for a and create a new project. Run firebase login and login with your previous created Firebase account.
For more information see .
To publish it at , run:
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). 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 .
Use the . You can find instructions in .
See the on how to deploy your react app to Modulus.
offers a zero-configuration single-command deployment. You can use now to deploy your app for free.
Install the now command-line tool either via the recommended or via node with npm install -g now.
Details are available in
See this on how to deploy your React app to Amazon Web Services and .
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 .
You can adjust various development and production settings by setting environment variables in your shell or with .
By default, Create React App will open the default system browser, favoring Chrome on macOS. Specify a 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.
Create React App assumes your application is hosted at the serving web server's root or a subpath as specified in . 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.
If the watcher doesn’t see a file called index.js and you’re referencing it by the folder name, you 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 .
If your project path contains parentheses, try moving the project to a path without them. This is caused by a .
On Linux and macOS, you might need to to allow more watchers.
If none of these solutions help please leave a comment .
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 installation as described in .
It is reported that installing Watchman 4.7.0 or newer fixes the issue. If you use , you can run these commands to update it:
You can find on the Watchman documentation page.
It is reported that npm run build can fail on machines with no swap space, which is common in cloud environments. If , consider adding some swap space to the machine you’re building on, or build the project locally.
This may be a problem with case sensitive filenames. Please refer to .
If you use a , 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 .
If you have ideas for more “How To” recipes that should be on this page, or
