How to resolve error: “[WDS] Disconnected!”

I fixed it like this;

as-is :

  entry: [
    "webpack-dev-server/client?http://localhost:9090",
    "webpack/hot/only-dev-server",
    "./src/app"
  ],

to-be :

  entry: [
    "webpack-dev-server/client?http://127.0.0.0:8080",
    "webpack/hot/only-dev-server",
    "./src"
  ],