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react-wheel-jank-demo

Demo of a React app that causes janky scrolling by attaching a wheel event to the entire document, even when it should only apply to a subsection of the page.

You can reproduce this using a mouse with a scroll wheel, and then trying to scroll on the entire document as well as within the smaller scrollable div.

Update: added touchstart events too, so you can reproduce jankiness on mobile browsers as well.

Test results

Test 1: wheel event, mousewheel scrolling, desktop browsers

Edge 14

No listeners React onWheel on inner div DOM wheel on inner div
Inner div scrolls smoothly ✔ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Chrome 52

No listeners React onWheel on inner div DOM wheel on inner div
Inner div scrolls smoothly ❌ Mac / ✔ Win ❌ ❌
Body scrolls smoothly ✔ ❌ ❌

Firefox 48

No listeners React onWheel on inner div DOM wheel on inner div
Inner div scrolls smoothly ❌ ❌ ❌
Body scrolls smoothly ❌ ❌ ❌

Firefox Dev Edition 50 w/ e10s (Mac)

No listeners React onWheel on inner div DOM wheel on inner div
Inner div scrolls smoothly ✔ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Safari 10

No listeners React onWheel on inner div DOM wheel on inner div
Inner div scrolls smoothly ❌ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Test 2: touchstart event, touch scrolling, mobile browsers

Edge 14 Mobile, Windows 10

No listeners React onTouchStart on inner div DOM touchstart on inner div
Inner div scrolls smoothly ✔ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Chrome 52, Android 7

No listeners React onTouchStart on inner div DOM touchstart on inner div
Inner div scrolls smoothly ✔ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Firefox 48, Android 7

No listeners React onTouchStart on inner div DOM touchstart on inner div
Inner div scrolls smoothly ✔ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Safari on iOS 9

No listeners React onTouchStart on inner div DOM touchstart on inner div
Inner div scrolls smoothly ❌ ❌ ❌
Body scrolls smoothly ✔ ❌ ✔

Build this app

There are multiple branches named v1, v2, etc., containing different versions of the app:

  1. No event listeners (Live version)
  2. React onWheel event on inner div (Live version)
  3. Vanilla DOM wheel event on inner div (Live version)
  4. React onTouchStart event on inner div (Live version)
  5. Vanilla DOM touchstart event on inner div (Live version)

To build the whole thing into the docs/ folder, do:

npm run build-all

To run a live demo and fiddle around with it, do:

npm start

Original create-react-app documentation follows

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

Table of Contents

Updating to New Releases

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’s delegates all the setup to react-scripts.

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

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

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

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

Sending Feedback

We are always open to your feedback.

Folder Structure

After creation, your project should look like this:

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

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

  • index.html is the page template;
  • favicon.ico is the icon you see in the browser tab;
  • 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.

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

Available Scripts

In the project directory, you can run:

npm start

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

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

npm run build

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

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

npm run eject

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

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

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

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

Displaying Lint Output in the Editor

Note: this feature is available with [email protected] and 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.

A note for Atom linter-eslint users

If you are using the Atom linter-eslint plugin, make sure that Use global ESLint installation option is checked:

Then make sure package.json of your project ends with this block:

{
  // ...
  "eslintConfig": {
    "extends": "./node_modules/react-scripts/config/eslint.js"
  }
}

Projects generated with [email protected] and higher should already have it.
If you don’t need ESLint integration with your editor, you can safely delete those three lines from your package.json.

Finally, you will need to install some packages globally:

npm install -g eslint babel-eslint eslint-plugin-react eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-flowtype

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

Installing a Dependency

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

npm install --save <library-name>

Importing a Component

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

For example:

Button.js

import React, { Component } from 'react';

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

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

DangerButton.js

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

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

export default DangerButton;

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

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

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

Learn more about ES6 modules:

Adding a Stylesheet

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

Button.css

.Button {
  padding: 20px;
}

Button.js

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

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

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

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

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

Post-Processing CSS

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

For example, this:

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

becomes this:

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

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

Adding Images and Fonts

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

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

Here is an example:

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

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

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

export default function Header;

This works in CSS too:

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

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

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

It is not required for React but many people enjoy it (and React Native uses a similar mechanism for images). However it may not be portable to some other environments, such as Node.js and Browserify. If you prefer to reference static assets in a more traditional way outside the module system, please let us know in this issue, and we will consider support for this.

Adding Bootstrap

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

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

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

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

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

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

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

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

Adding Flow

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

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

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

src/App.js:3
  3: import logo from './logo.svg';
                      ^^^^^^^^^^^^ ./logo.svg. Required module not found

src/App.js:4
  4: import './App.css';
            ^^^^^^^^^^^ ./App.css. Required module not found

src/index.js:5
  5: import './index.css';
            ^^^^^^^^^^^^^ ./index.css. Required module not found

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

[libs]
./node_modules/fbjs/flow/lib

[options]
esproposal.class_static_fields=enable
esproposal.class_instance_fields=enable

module.name_mapper='^\(.*\)\.css$' -> 'react-scripts/config/flow/css'
module.name_mapper='^\(.*\)\.\(jpg\|png\|gif\|eot\|otf\|webp\|svg\|ttf\|woff\|woff2\|mp4\|webm\)$' -> 'react-scripts/config/flow/file'

suppress_type=$FlowIssue
suppress_type=$FlowFixMe

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

If you later eject, you’ll need to replace react-scripts references with the <PROJECT_ROOT> placeholder, for example:

module.name_mapper='^\(.*\)\.css$' -> '<PROJECT_ROOT>/config/flow/css'
module.name_mapper='^\(.*\)\.\(jpg\|png\|gif\|eot\|otf\|webp\|svg\|ttf\|woff\|woff2\|mp4\|webm\)$' -> '<PROJECT_ROOT>/config/flow/file'

We will consider integrating more tightly with Flow in the future so that you don’t have to do this.

Adding Custom Environment Variables

Note: this feature is available with [email protected] and 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, in addition to process.env.NODE_ENV.

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

First, you need to have environment variables defined, which can vary between OSes. For example, let's say you wanted to consume a secret defined in the environment inside a <form>:

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

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:

Windows (cmd.exe)

set REACT_APP_SECRET_CODE=abcdef&&npm start

(Note: the lack of whitespace is intentional.)

Linux, OS X (Bash)

REACT_APP_SECRET_CODE=abcdef npm start

Note: Defining environment variables in this manner is temporary for the life of the shell session. Setting permanent environment variables is outside the scope of these docs.

With our environment variable defined, we start the app and consume the values. Remember that the NODE_ENV variable will be set for you automatically. When you load the app in the browser and inspect the <input>, you will see its value set to abcdef, and the bold text will show the environment provided when using npm start:

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

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

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

Integrating with a Node Backend

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

Proxying API Requests in Development

Note: this feature is available with [email protected] and 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:

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

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

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

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

This way, when you fetch('/api/todos') in development, the development server will recognize that it’s not a static asset, and will proxy your request to http://localhost:4000/api/todos as a fallback.

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

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

Keep in mind that proxy only has effect in development (with npm start), and it 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 will be redirected to the specified proxy.

Currently the proxy option only handles HTTP requests, and it won’t proxy WebSocket connections.
If the proxy option is not flexible enough for you, alternatively you can:

Deployment

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:

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

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

Now

See this example for a zero-configuration single-command deployment with now.

Heroku

Use the Heroku Buildpack for Create React App.
You can find instructions in Deploying React with Zero Configuration.

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.

              email: [email protected]
           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 protected]
         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.

GitHub Pages

Note: this feature is available with [email protected] and higher.

Open your package.json and add a homepage field:

  "homepage": "http://myusername.github.io/my-app",

The above step is important!
Create React App uses the homepage field to determine the root URL in the built HTML file.

Now, whenever you run npm run build, you will see a cheat sheet with a sequence of commands to deploy to GitHub pages:

git commit -am "Save local changes"
git checkout -B gh-pages
git add -f build
git commit -am "Rebuild website"
git filter-branch -f --prune-empty --subdirectory-filter build
git push -f origin gh-pages
git checkout -

You may copy and paste them, or put them into a custom shell script. You may also customize them for another hosting provider.

Note that 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 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.

Something Missing?

If you have ideas for more “How To” recipes that should be on this page, let us know or contribute some!