; + } +} +``` + +**This is not required for React** but many people find this feature convenient. You can read about the benefits of this approach [here](https://medium.com/seek-ui-engineering/block-element-modifying-your-javascript-components-d7f99fcab52b). 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](https://github.com/postcss/autoprefixer) so you don’t need to worry about it. + +For example, this: + +```css +.App { + display: flex; + flex-direction: row; + align-items: center; +} +``` + +becomes this: + +```css +.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: + +```js +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

; +} + +export default Header; +``` + +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: + +```css +.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).
+An alternative way of handling static assets is described in the next section. + +## Using the `public` Folder + +>Note: this feature is available with `react-scripts@0.5.0` and higher. + +Normally we encourage you to `import` assets in JavaScript files as described above. This mechanism provides a number of benefits: + +* 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: + +```html + +``` + +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: + +```js +render() { + // Note: this is an escape hatch and should be used sparingly! + // Normally we recommend using `import` for getting asset URLs + // as described in “Adding Images and Fonts” above this section. + return

; +} +``` + +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. + +However, it can be handy for referencing assets like [`manifest.webmanifest`](https://developer.mozilla.org/en-US/docs/Web/Manifest) from HTML, or including small scripts like [`pace.js`](http://github.hubspot.com/pace/docs/welcome/) outside of the bundled code. + +Note that if you add a `