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- <div align="center">
- <a href="https://github.com/webpack/webpack">
- <img width="200" height="200" src="https://webpack.js.org/assets/icon-square-big.svg">
- </a>
- </div>
-
- [![npm][npm]][npm-url]
- [![node][node]][node-url]
- [![deps][deps]][deps-url]
- [![tests][tests]][tests-url]
- [![coverage][cover]][cover-url]
- [![chat][chat]][chat-url]
- [![size][size]][size-url]
-
- # webpack-dev-middleware
-
- An express-style development middleware for use with [webpack](https://webpack.js.org)
- bundles and allows for serving of the files emitted from webpack.
- This should be used for **development only**.
-
- Some of the benefits of using this middleware include:
-
- - No files are written to disk, rather it handles files in memory
- - If files changed in watch mode, the middleware delays requests until compiling
- has completed.
- - Supports hot module reload (HMR).
-
- ## Requirements
-
- This module requires a minimum of Node v6.9.0 and Webpack v4.0.0, and must be used with a
- server that accepts express-style middleware.
-
- ## Getting Started
-
- First thing's first, install the module:
-
- ```console
- npm install webpack-dev-middleware --save-dev
- ```
-
- _Note: We do not recommend installing this module globally._
-
- ## Usage
-
- ```js
- const webpack = require('webpack');
- const middleware = require('webpack-dev-middleware');
- const compiler = webpack({
- // webpack options
- });
- const express = require('express');
- const app = express();
-
- app.use(
- middleware(compiler, {
- // webpack-dev-middleware options
- })
- );
-
- app.listen(3000, () => console.log('Example app listening on port 3000!'));
- ```
-
- ## Options
-
- The middleware accepts an `options` Object. The following is a property reference
- for the Object.
-
- _Note: The `publicPath` property is required, whereas all other options are optional_
-
- ### methods
-
- Type: `Array`
- Default: `[ 'GET', 'HEAD' ]`
-
- This property allows a user to pass the list of HTTP request methods accepted by the server.
-
- ### headers
-
- Type: `Object`
- Default: `undefined`
-
- This property allows a user to pass custom HTTP headers on each request. eg.
- `{ "X-Custom-Header": "yes" }`
-
- ### index
-
- Type: `String`
- Default: `undefined`
-
- "index.html",
- // The index path for web server, defaults to "index.html".
- // If falsy (but not undefined), the server will not respond to requests to the root URL.
-
- ### lazy
-
- Type: `Boolean`
- Default: `undefined`
-
- This option instructs the module to operate in 'lazy' mode, meaning that it won't
- recompile when files change, but rather on each request.
-
- ### logger
-
- Type: `Object`
- Default: [`webpack-log`](https://github.com/webpack-contrib/webpack-log/blob/master/index.js)
-
- In the rare event that a user would like to provide a custom logging interface,
- this property allows the user to assign one. The module leverages
- [`webpack-log`](https://github.com/webpack-contrib/webpack-log#readme)
- for creating the [`loglevelnext`](https://github.com/shellscape/loglevelnext#readme)
- logging management by default. Any custom logger must adhere to the same
- exports for compatibility. Specifically, all custom loggers must have the
- following exported methods at a minimum:
-
- - `log.trace`
- - `log.debug`
- - `log.info`
- - `log.warn`
- - `log.error`
-
- Please see the documentation for `loglevel` for more information.
-
- ### logLevel
-
- Type: `String`
- Default: `'info'`
-
- This property defines the level of messages that the module will log. Valid levels
- include:
-
- - `trace`
- - `debug`
- - `info`
- - `warn`
- - `error`
- - `silent`
-
- Setting a log level means that all other levels below it will be visible in the
- console. Setting `logLevel: 'silent'` will hide all console output. The module
- leverages [`webpack-log`](https://github.com/webpack-contrib/webpack-log#readme)
- for logging management, and more information can be found on its page.
-
- ### logTime
-
- Type: `Boolean`
- Default: `false`
-
- If `true` the log output of the module will be prefixed by a timestamp in the
- `HH:mm:ss` format.
-
- ### mimeTypes
-
- Type: `Object`
- Default: `null`
-
- This property allows a user to register custom mime types or extension mappings.
- eg. `mimeTypes: { 'text/html': [ 'phtml' ] }`.
-
- By default node-mime will throw an error if you try to map a type to an extension
- that is already assigned to another type. Passing `force: true` will suppress this behavior
- (overriding any previous mapping).
- eg. `mimeTypes: { typeMap: { 'text/html': [ 'phtml' ] } }, force: true }`.
-
- Please see the documentation for
- [`node-mime`](https://github.com/broofa/node-mime#mimedefinetypemap-force--false) for more information.
-
- ### publicPath
-
- Type: `String`
- _Required_
-
- The public path that the middleware is bound to. _Best Practice: use the same
- `publicPath` defined in your webpack config. For more information about
- `publicPath`, please see
- [the webpack documentation](https://webpack.js.org/guides/public-path)._
-
- ### reporter
-
- Type: `Object`
- Default: `undefined`
-
- Allows users to provide a custom reporter to handle logging within the module.
- Please see the [default reporter](/lib/reporter.js)
- for an example.
-
- ### serverSideRender
-
- Type: `Boolean`
- Default: `undefined`
-
- Instructs the module to enable or disable the server-side rendering mode. Please
- see [Server-Side Rendering](#server-side-rendering) for more information.
-
- ### stats
-
- Type: `Object`
- Default: `{ context: process.cwd() }`
-
- Options for formatting statistics displayed during and after compile. For more
- information and property details, please see the
- [webpack documentation](https://webpack.js.org/configuration/stats/#stats).
-
- ### watchOptions
-
- Type: `Object`
- Default: `{ aggregateTimeout: 200 }`
-
- The module accepts an `Object` containing options for file watching, which is
- passed directly to the compiler provided. For more information on watch options
- please see the [webpack documentation](https://webpack.js.org/configuration/watch/#watchoptions)
-
- ### writeToDisk
-
- Type: `Boolean|Function`
- Default: `false`
-
- If `true`, the option will instruct the module to write files to the configured
- location on disk as specified in your `webpack` config file. _Setting
- `writeToDisk: true` won't change the behavior of the `webpack-dev-middleware`,
- and bundle files accessed through the browser will still be served from memory._
- This option provides the same capabilities as the
- [`WriteFilePlugin`](https://github.com/gajus/write-file-webpack-plugin/pulls).
-
- This option also accepts a `Function` value, which can be used to filter which
- files are written to disk. The function follows the same premise as
- [`Array#filter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter)
- in which a return value of `false` _will not_ write the file, and a return value
- of `true` _will_ write the file to disk. eg.
-
- ```js
- {
- writeToDisk: (filePath) => {
- return /superman\.css$/.test(filePath);
- };
- }
- ```
-
- ### fs
-
- Type: `Object`
- Default: `MemoryFileSystem`
-
- Set the default file system which will be used by webpack as primary destination of generated files. Default is set to webpack's default file system: [memory-fs](https://github.com/webpack/memory-fs). This option isn't affected by the [writeToDisk](#writeToDisk) option.
-
- **Note:** As of 3.5.x version of the middleware you have to provide `.join()` method to the `fs` instance manually. This can be done simply by using `path.join`:
-
- ```js
- fs.join = path.join; // no need to bind
- ```
-
- ## API
-
- `webpack-dev-middleware` also provides convenience methods that can be use to
- interact with the middleware at runtime:
-
- ### `close(callback)`
-
- Instructs a webpack-dev-middleware instance to stop watching for file changes.
-
- ### Parameters
-
- #### callback
-
- Type: `Function`
-
- A function executed once the middleware has stopped watching.
-
- ### `invalidate()`
-
- Instructs a webpack-dev-middleware instance to recompile the bundle.
- e.g. after a change to the configuration.
-
- ```js
- const webpack = require('webpack');
- const compiler = webpack({ ... });
- const middleware = require('webpack-dev-middleware');
- const instance = middleware(compiler);
-
- app.use(instance);
-
- setTimeout(() => {
- // After a short delay the configuration is changed and a banner plugin is added
- // to the config
- compiler.apply(new webpack.BannerPlugin('A new banner'));
-
- // Recompile the bundle with the banner plugin:
- instance.invalidate();
- }, 1000);
- ```
-
- ### `waitUntilValid(callback)`
-
- Executes a callback function when the compiler bundle is valid, typically after
- compilation.
-
- ### Parameters
-
- #### callback
-
- Type: `Function`
-
- A function executed when the bundle becomes valid. If the bundle is
- valid at the time of calling, the callback is executed immediately.
-
- ```js
- const webpack = require('webpack');
- const compiler = webpack({ ... });
- const middleware = require('webpack-dev-middleware');
- const instance = middleware(compiler);
-
- app.use(instance);
-
- instance.waitUntilValid(() => {
- console.log('Package is in a valid state');
- });
- ```
-
- ## Known Issues
-
- ### Multiple Successive Builds
-
- Watching (by means of `lazy: false`) will frequently cause multiple compilations
- as the bundle changes during compilation. This is due in part to cross-platform
- differences in file watchers, so that webpack doesn't loose file changes when
- watched files change rapidly. If you run into this situation, please make use of
- the [`TimeFixPlugin`](https://github.com/egoist/time-fix-plugin).
-
- ## Server-Side Rendering
-
- _Note: this feature is experimental and may be removed or changed completely in the future._
-
- In order to develop an app using server-side rendering, we need access to the
- [`stats`](https://github.com/webpack/docs/wiki/node.js-api#stats), which is
- generated with each build.
-
- With server-side rendering enabled, `webpack-dev-middleware` sets the `stat` to
- `res.locals.webpackStats` and the memory filesystem to `res.locals.fs` before invoking the next middleware, allowing a
- developer to render the page body and manage the response to clients.
-
- _Note: Requests for bundle files will still be handled by
- `webpack-dev-middleware` and all requests will be pending until the build
- process is finished with server-side rendering enabled._
-
- Example Implementation:
-
- ```js
- const webpack = require('webpack');
- const compiler = webpack({
- // webpack options
- });
- const isObject = require('is-object');
- const middleware = require('webpack-dev-middleware');
-
- // This function makes server rendering of asset references consistent with different webpack chunk/entry configurations
- function normalizeAssets(assets) {
- if (isObject(assets)) {
- return Object.values(assets);
- }
-
- return Array.isArray(assets) ? assets : [assets];
- }
-
- app.use(middleware(compiler, { serverSideRender: true }));
-
- // The following middleware would not be invoked until the latest build is finished.
- app.use((req, res) => {
- const assetsByChunkName = res.locals.webpackStats.toJson().assetsByChunkName;
- const fs = res.locals.fs;
- const outputPath = res.locals.webpackStats.toJson().outputPath;
-
- // then use `assetsByChunkName` for server-sider rendering
- // For example, if you have only one main chunk:
- res.send(`
- <html>
- <head>
- <title>My App</title>
- <style>
- ${normalizeAssets(assetsByChunkName.main)
- .filter((path) => path.endsWith('.css'))
- .map((path) => fs.readFileSync(outputPath + '/' + path))
- .join('\n')}
- </style>
- </head>
- <body>
- <div id="root"></div>
- ${normalizeAssets(assetsByChunkName.main)
- .filter((path) => path.endsWith('.js'))
- .map((path) => `<script src="${path}"></script>`)
- .join('\n')}
- </body>
- </html>
- `);
- });
- ```
-
- ## Support
-
- We do our best to keep Issues in the repository focused on bugs, features, and
- needed modifications to the code for the module. Because of that, we ask users
- with general support, "how-to", or "why isn't this working" questions to try one
- of the other support channels that are available.
-
- Your first-stop-shop for support for webpack-dev-server should by the excellent
- [documentation][docs-url] for the module. If you see an opportunity for improvement
- of those docs, please head over to the [webpack.js.org repo][wjo-url] and open a
- pull request.
-
- From there, we encourage users to visit the [webpack Gitter chat][chat-url] and
- talk to the fine folks there. If your quest for answers comes up dry in chat,
- head over to [StackOverflow][stack-url] and do a quick search or open a new
- question. Remember; It's always much easier to answer questions that include your
- `webpack.config.js` and relevant files!
-
- If you're twitter-savvy you can tweet [#webpack][hash-url] with your question
- and someone should be able to reach out and lend a hand.
-
- If you have discovered a :bug:, have a feature suggestion, or would like to see
- a modification, please feel free to create an issue on Github. _Note: The issue
- template isn't optional, so please be sure not to remove it, and please fill it
- out completely._
-
- ## Contributing
-
- Please take a moment to read our contributing guidelines if you haven't yet done so.
-
- [CONTRIBUTING](./.github/CONTRIBUTING.md)
-
- ## License
-
- [MIT](./LICENSE)
-
- [npm]: https://img.shields.io/npm/v/webpack-dev-middleware.svg
- [npm-url]: https://npmjs.com/package/webpack-dev-middleware
- [node]: https://img.shields.io/node/v/webpack-dev-middleware.svg
- [node-url]: https://nodejs.org
- [deps]: https://david-dm.org/webpack/webpack-dev-middleware.svg
- [deps-url]: https://david-dm.org/webpack/webpack-dev-middleware
- [tests]: https://dev.azure.com/webpack/webpack-dev-middleware/_apis/build/status/webpack.webpack-dev-middleware?branchName=master
- [tests-url]: https://dev.azure.com/webpack/webpack-dev-middleware/_build/latest?definitionId=8&branchName=master
- [cover]: https://codecov.io/gh/webpack/webpack-dev-middleware/branch/master/graph/badge.svg
- [cover-url]: https://codecov.io/gh/webpack/webpack-dev-middleware
- [chat]: https://badges.gitter.im/webpack/webpack.svg
- [chat-url]: https://gitter.im/webpack/webpack
- [size]: https://packagephobia.now.sh/badge?p=webpack-dev-middleware
- [size-url]: https://packagephobia.now.sh/result?p=webpack-dev-middleware
- [docs-url]: https://webpack.js.org/guides/development/#using-webpack-dev-middleware
- [hash-url]: https://twitter.com/search?q=webpack
- [middleware-url]: https://github.com/webpack/webpack-dev-middleware
- [stack-url]: https://stackoverflow.com/questions/tagged/webpack-dev-middleware
- [uglify-url]: https://github.com/webpack-contrib/uglifyjs-webpack-plugin
- [wjo-url]: https://github.com/webpack/webpack.js.org
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