DevServer

DevServer

webpack-dev-server can be used to quickly develop an application. See the "How to Develop?" to get started.

This page describes the options that affect the behavior of webpack-dev-server (short: dev-server).

Options that are compatible with webpack-dev-middleware have ???? next to them.

devServer

object

This set of options is picked up by webpack-dev-server and can be used to change its behavior in various ways. Here's a simple example that gzips and serves everything from our dist/ directory:

devServer: {
  contentBase: path.join(__dirname, "dist"),
  compress: true,
  port: 9000
}

When the server is started, there will be a message prior to the list of resolved modules:

http://localhost:9000/
webpack result is served from /build/
content is served from dist/

that will give some background on where the server is located and what it's serving.

If you're using dev-server through the Node.js API, the options in devServer will be ignored. Pass the options as a second parameter instead: new WebpackDevServer(compiler, {...}). See here for an example of how to use webpack-dev-server through the Node.js API.

Be aware that when exporting multiple configurations only the devServer options for the first configuration will be taken into account and used for all the configurations in the array.

If you're having trouble, navigating to the /webpack-dev-server route will show where files are served. For example, http://localhost:9000/webpack-dev-server.

devServer.allowedHosts

array

This option allows you to specify a whitelist of hosts that are allowed to access the dev server.

allowedHosts: [
    'host.com',
    'subdomain.host.com',
    'subdomain2.host.com',
    'host2.com'
]

Mimicking django's ALLOWED_HOSTS, a value beginning with . can be used as a subdomain wildcard. .host.com will match host.com, www.host.com, and any other subdomain of host.com.

// this achieves the same effect as the first example
// with the bonus of not having to update your config
// if new subdomains need to access the dev server
allowedHosts: [
    '.host.com',
    'host2.com'
]

devServer.clientLogLevel

string

When using inline mode, the console in your DevTools will show you messages e.g. before reloading, before an error or when Hot Module Replacement is enabled. This may be too verbose.

You can prevent all these messages from showing, by using this option:

clientLogLevel: "none"

Possible values are none, error, warning or info (default).

Note that the console will always show bundle errors and warnings. This option only effects the message before it.

devServer.compress

boolean

Enable gzip compression for everything served:

compress: true

devServer.contentBase

boolean string array

Tell the server where to serve content from. This is only necessary if you want to serve static files. devServer.publicPath will be used to determine where the bundles should be served from, and takes precedence.

By default it will use your current working directory to serve content, but you can modify this to another directory:

contentBase: path.join(__dirname, "public")

Note that it is recommended to use an absolute path.

It is also possible to serve from multiple directories:

contentBase: [path.join(__dirname, "public"), path.join(__dirname, "assets")]

To disable contentBase:

contentBase: false

devServer.filename ????

string

This option lets you reduce the compilations in lazy mode. By default in lazy mode, every request results in a new compilation. With filename, it's possible to only compile when a certain file is requested.

If output.filename is set to bundle.js and filename is used like this:

lazy: true,
filename: "bundle.js"

It will now only compile the bundle when /bundle.js is requested.

filename has no effect when used without lazy mode.

devServer.headers ????

object

Adds headers to all responses:

headers: {
  "X-Custom-Foo": "bar"
}

devServer.historyApiFallback

boolean object

When using the HTML5 History API, the index.html page will likely have to be served in place of any 404 responses. Enable this by passing:

historyApiFallback: true

By passing an object this behavior can be controlled further using options like rewrites:

historyApiFallback: {
  rewrites: [
    { from: /^\/$/, to: '/views/landing.html' },
    { from: /^\/subpage/, to: '/views/subpage.html' },
    { from: /./, to: '/views/404.html' }
  ]
}

When using dots in your path (common with Angular), you may need to use the disableDotRule:

historyApiFallback: {
  disableDotRule: true
}

For more options and information, see the connect-history-api-fallback documentation.

devServer.host - CLI only

string

Specify a host to use. By default this is localhost. If you want your server to be accessible externally, specify it like this:

host: "0.0.0.0"

devServer.hot

boolean

Enable webpack's Hot Module Replacement feature:

hot: true

Note that you must also include a new webpack.HotModuleReplacementPlugin() to fully enable HMR. See the HMR concepts page for more information.

devServer.hotOnly - CLI only

boolean

Enables Hot Module Replacement (see devServer.hot) without page refresh as fallback in case of build failures.

hotOnly: true

devServer.https

boolean object

By default dev-server will be served over HTTP. It can optionally be served over HTTP/2 with HTTPS:

https: true

With the above setting a self-signed certificate is used, but you can provide your own:

https: {
  key: fs.readFileSync("/path/to/server.key"),
  cert: fs.readFileSync("/path/to/server.crt"),
  ca: fs.readFileSync("/path/to/ca.pem"),
}

This object is passed straight to Node.js HTTPS module, so see the HTTPS documentation for more information.

devServer.inline - CLI only

boolean

Toggle between the dev-server's two different modes. By default the application will be served with inline mode enabled. This means that a script will be inserted in your bundle to take care of live reloading, and build messages will appear in the browser console.

It is also possible to use iframe mode, which uses an <iframe> under a notification bar with messages about the build. To switch to iframe mode:

inline: false

Inline mode is recommended when using Hot Module Replacement.

devServer.lazy ????

boolean

When lazy is enabled, the dev-server will only compile the bundle when it gets requested. This means that webpack will not watch any file changes. We call this lazy mode.

lazy: true

watchOptions will have no effect when used with lazy mode.

If you use the CLI, make sure inline mode is disabled.

devServer.noInfo ????

boolean

With noInfo enabled, messages like the webpack bundle information that is shown when starting up and after each save, will be hidden. Errors and warnings will still be shown.

noInfo: true

devServer.overlay

boolean object

Shows a full-screen overlay in the browser when there are compiler errors or warnings. Disabled by default. If you want to show only compiler errors:

overlay: true

If you want to show warnings as well as errors:

overlay: {
  warnings: true,
  errors: true
}

devServer.port - CLI only

number

Specify a port number to listen for requests on:

port: 8080

devServer.proxy

object

Proxying some URLs can be useful when you have a separate API backend development server and you want to send API requests on the same domain.

The dev-server makes use of the powerful http-proxy-middleware package. Checkout its documentation for more advanced usages.

With a backend on localhost:3000, you can use this to enable proxying:

proxy: {
  "/api": "http://localhost:3000"
}

A request to /api/users will now proxy the request to http://localhost:3000/api/users.

If you don't want /api to be passed along, we need to rewrite the path:

proxy: {
  "/api": {
    target: "http://localhost:3000",
    pathRewrite: {"^/api" : ""}
  }
}

A backend server running on HTTPS with an invalid certificate will not be accepted by default. If you want to, modify your config like this:

proxy: {
  "/api": {
    target: "https://other-server.example.com",
    secure: false
  }
}

Sometimes you don't want to proxy everything. It is possible to bypass the proxy based on the return value of a function.

In the function you get access to the request, response and proxy options. It must return either false or a path that will be served instead of continuing to proxy the request.

E.g. for a browser request, you want to serve a HTML page, but for an API request you want to proxy it. You could do something like this:

proxy: {
  "/api": {
    target: "http://localhost:3000",
    bypass: function(req, res, proxyOptions) {
      if (req.headers.accept.indexOf("html") !== -1) {
        console.log("Skipping proxy for browser request.");
        return "/index.html";
      }
    }
  }
}

devServer.progress - CLI only

boolean

Output running progress to console.

devServer.public - CLI only

string

When using inline mode and you're proxying dev-server, the inline client script does not always know where to connect to. It will try to guess the URL of the server based on window.location, but if that fails you'll need to use this.

For example, the dev-server is proxied by nginx, and available on myapp.test:

public: "myapp.test:80"

devServer.publicPath ????

string

The bundled files will be available in the browser under this path.

Imagine that the server is running under http://localhost:8080 and output.filename is set to bundle.js. By default the publicPath is "/", so your bundle is available as http://localhost:8080/bundle.js.

The publicPath can be changed so the bundle is put in a directory:

publicPath: "/assets/"

The bundle will now be available as http://localhost:8080/assets/bundle.js.

Make sure publicPath always starts and ends with a forward slash.

It is also possible to use a full URL. This is necessary for Hot Module Replacement.

publicPath: "http://localhost:8080/assets/"

The bundle will also be available as http://localhost:8080/assets/bundle.js.

It is recommended that devServer.publicPath is the same as output.publicPath.

devServer.quiet ????

boolean

With quiet enabled, nothing except the initial startup information will be written to the console. This also means that errors or warnings from webpack are not visible.

quiet: true

devServer.setup

function

Here you can access the Express app object and add your own custom middleware to it. For example, to define custom handlers for some paths:

setup(app){
  app.get('/some/path', function(req, res) {
    res.json({ custom: 'response' });
  });
}

devServer.staticOptions

It is possible to configure advanced options for serving static files from contentBase. See the Express documentation for the possible options. An example:

staticOptions: {
  redirect: false
}

This only works when using contentBase as a string.

devServer.stats ????

string object

This option lets you precisely control what bundle information gets displayed. This can be a nice middle ground if you want some bundle information, but not all of it.

To show only errors in your bundle:

stats: "errors-only"

For more information, see the stats documentation.

This option has no effect when used with quiet or noInfo.

devServer.watchContentBase

boolean

Tell the server to watch the files served by the devServer.contentBase option. File changes will trigger a full page reload.

watchContentBase: true

It is disabled by default.

devServer.watchOptions ????

object

Control options related to watching the files.

webpack uses the file system to get notified of file changes. In some cases this does not work. For example, when using Network File System (NFS). Vagrant also has a lot of problems with this. In these cases, use polling:

watchOptions: {
  poll: true
}

If this is too heavy on the file system, you can change this to an integer to set the interval in milliseconds.

See WatchOptions for more options.