I've just come across the same problem.

As webpack v4 is still in alpha, I guess there is some decisions to be made about how else to handle this i.e. it's probably premature to roll this out now, but perhaps a webpack-dev-server v3-beta might be useful with note around people trying webpack v4?

Should this PR also update the peerDependencies from the package.json also?

Hi @shellscape (sorry for at'ing you directly!) but I was wondering if it was realised that this prevents people from trying out anything greater than webpack v4-alpha.0? (i.e. alpha.1+ wont' work).

I saw some other issues already mentioning v3-beta but i could not see a branch or release with those tags. Would v3 fix this issue and Is v3 available for testing?

Any chance this patch could be released as a beta version so it can be tested alongside the webpack 4 beta?

To test this pull request, you can put it directly in your package.json

"devDependencies": {
   "webpack": "^4.0.0-beta.0",
   "webpack-cli": "^2.0.4",
   "webpack-dev-server": "github:donaldpipowitch/webpack-dev-server#patch-1"
 },

I executed it and it didn't work.

 $ ./node_modules/.bin/webpack-dev-server
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
 - configuration.entry should be one of these:
   object { <key>: non-empty string | [non-empty string] } | non-empty string | [non-empty string] | function
   -> The entry point(s) of the compilation.
   Details:
    * configuration.entry should be an object.
      -> Multiple entry bundles are created. The key is the chunk name. The value can be a string or an array.
    * configuration.entry should be a string.
      -> An entry point without name. The string is resolved to a module which is loaded upon startup.
    * configuration.entry[1] should be a string.
      -> A non-empty string
    * configuration.entry should be an instance of function
      -> A Function returning an entry object, an entry string, an entry array or a promise to these things.

I dont know if I'm correctly understanding it, but It seems that it is asking for a configuration when webpack4 doesn't have one in the first place. 🤷

Please test the latest beta, webpack-dev-server@3.0.0-beta.1. Also be sure to read the changelog.

Amazing, thanks guys!!
for anyone else, this now works with my current test setup of:

    "webpack": "^4.0.0-beta.1",
    "webpack-cli": "^2.0.6",
    "webpack-dev-server": "^3.0.0-beta.1",