webpack-dev-middleware

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webpack-dev-middleware

An express-style development middleware for use with webpack 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).

Getting Started

First thing's first, install the module:

npm install webpack-dev-middleware --save-dev

[!WARNING]

We do not recommend installing this module globally.

Usage

const express = require("express");
const webpack = require("webpack");
const middleware = require("webpack-dev-middleware");

const compiler = webpack({
  // webpack options
});

const app = express();

app.use(
  middleware(compiler, {
    // webpack-dev-middleware options
  }),
);

app.listen(3000, () => console.log("Example app listening on port 3000!"));

See below for an example of use with fastify.

Options

The middleware accepts an options Object. The following is a property reference for the Object.

methods

Type: Array
Default: [ 'GET', 'HEAD' ]

This property allows a user to pass the list of HTTP request methods accepted by the middleware**.

headers

Type: Array|Object|Function Default: undefined

This property allows a user to pass custom HTTP headers on each request. eg. { "X-Custom-Header": "yes" }

or

webpackDevMiddleware(compiler, {
  headers: () => ({
    "Last-Modified": new Date(),
  }),
});

or

webpackDevMiddleware(compiler, {
  headers: (req, res, context) => {
    res.setHeader("Last-Modified", new Date());
  },
});

or

webpackDevMiddleware(compiler, {
  headers: [
    {
      key: "X-custom-header",
      value: "foo",
    },
    {
      key: "Y-custom-header",
      value: "bar",
    },
  ],
});

or

webpackDevMiddleware(compiler, {
  headers: () => [
    {
      key: "X-custom-header",
      value: "foo",
    },
    {
      key: "Y-custom-header",
      value: "bar",
    },
  ],
});

index

Type: Boolean|String Default: index.html

If false (but not undefined), the server will not respond to requests to the root URL.

mimeTypes

Type: Object
Default: undefined

This property allows a user to register custom mime types or extension mappings. eg. mimeTypes: { phtml: 'text/html' }.

Please see the documentation for mime-types for more information.

mimeTypeDefault

Type: String
Default: undefined

This property allows a user to register a default mime type when we can't determine the content type.

etag

Type: "weak" | "strong"
Default: undefined

Enable or disable etag generation. Boolean value use

lastModified

Type: Boolean Default: undefined

Enable or disable Last-Modified header. Uses the file system's last modified value.

cacheControl

Type: Boolean | Number | String | { maxAge?: number, immutable?: boolean } Default: undefined

Depending on the setting, the following headers will be generated:

• Boolean - Cache-Control: public, max-age=31536000000
• Number - Cache-Control: public, max-age=YOUR_NUMBER
• String - Cache-Control: YOUR_STRING
• { maxAge?: number, immutable?: boolean } - Cache-Control: public, max-age=YOUR_MAX_AGE_or_31536000000, also , immutable can be added if you set the immutable option to true

Enable or disable setting Cache-Control response header.

cacheImmutable

Type: Boolean Default: undefined

Enable or disable setting Cache-Control: public, max-age=31536000, immutable response header for immutable assets (i.e. asset with a hash like image.a4c12bde.jpg). Immutable assets are assets that have their hash in the file name therefore they can be cached, because if you change their contents the file name will be changed. Take preference over the cacheControl option if the asset was defined as immutable.

publicPath

Type: String Default: output.publicPath (from a configuration)

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.

stats

Type: Boolean|String|Object Default: stats (from a configuration)

Stats options object or preset name.

serverSideRender

Type: Boolean
Default: undefined

Instructs the module to enable or disable the server-side rendering mode. Please see Server-Side Rendering for more information.

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.

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 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.

const webpack = require("webpack");

const configuration = {/* Webpack configuration */};
const compiler = webpack(configuration);

middleware(compiler, {
  writeToDisk: (filePath) => /superman\.css$/.test(filePath),
});

outputFileSystem

Type: Object
Default: memfs

Set the default file system which will be used by webpack as primary destination of generated files. This option isn't affected by the writeToDisk option.

You have to provide .join() and mkdirp method to the outputFileSystem instance manually for compatibility with webpack@4.

This can be done simply by using path.join:

const path = require("node:path");
const mkdirp = require("mkdirp");
const myOutputFileSystem = require("my-fs");
const webpack = require("webpack");

myOutputFileSystem.join = path.join.bind(path); // no need to bind
myOutputFileSystem.mkdirp = mkdirp.bind(mkdirp); // no need to bind

const compiler = webpack({/* Webpack configuration */});

middleware(compiler, { outputFileSystem: myOutputFileSystem });

modifyResponseData

Allows to set up a callback to change the response data.

const webpack = require("webpack");

const configuration = {/* Webpack configuration