The script has an unsupported MIME type ('text/html')

Hi I’ve written a small project with create-react-app, it runs in the browser ‘http://localhost:3000/’ with ‘npm start’ but i’m seeing these two errors in the console:

The script has an unsupported MIME type ('text/html').  :3000/service-worker.js:1
GET http://localhost:3000/service-worker.js net::ERR_INSECURE_RESPONSE  :3000/service-worker.js:1

this is my package.json

{
  "name": "my-app",
  "version": "0.1.0",
  "private": true,
  "devDependencies": {
    "react-scripts": "0.4.1"
  },
  "dependencies": {
    "react": "^15.3.1",
    "react-dom": "^15.3.1",
    "react-redux": "^4.4.5",
    "redux": "^3.6.0"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test --env=jsdom",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "./node_modules/react-scripts/config/eslint.js"
  },
  "standard": {
    "globals": [
      "describe",
      "context",
      "before",
      "beforeEach",
      "after",
      "afterEach",
      "it",
      "expect"
    ]
  }
}

[n3tr]

Maybe I’m wrong, the error is about service worker has been register for localhost:3000.

Can you open Chrome Dev Tools -> Application -> Service Worker and see if you have a service worker has been registered? If yes click unregister and refresh the page again.

[rob-yoti]

I got this issue after running npm run build on a new app, and moving the build folder to my express application which then served it.

It appears the helmet middleware was interfering with the client side caching, so if you have this issue on a node server, it may be worth checking this.