$ yarn add webpack webpack-dev-server
...
Done in 6.34s.
$ node_modules/.bin/webpack-dev-server 
No configuration file found and no entry configured via CLI option.
When using the CLI you need to provide at least two arguments: entry and output.
A configuration file could be named 'webpack.config.js' in the current directory.
Use --help to display the CLI options.
# This indicates the module installed properly.
$ rm -rf node_modules
$ yarn install --ignore-optional
$ node_modules/.bin/webpack-dev-server 
module.js:538
    throw err;
    ^

Error: Cannot find module 'fs.realpath'
    at Function.Module._resolveFilename (module.js:536:15)
    at Function.Module._load (module.js:466:25)
    at Module.require (module.js:579:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/Users/benesch/Desktop/t/node_modules/glob/glob.js:44:10)
    at Module._compile (module.js:635:30)
    at Object.Module._extensions..js (module.js:646:10)
    at Module.load (module.js:554:32)
    at tryModuleLoad (module.js:497:12)
    at Function.Module._load (module.js:489:3)