Support for the experimental syntax 'classProperties' isn't currently enabled

While I was setting up React within Django project I came across this error

ModuleBuildError in Module build failed (from ./node_modules/babel-loader/lib/index.js): SyntaxError: C:\Users\1Sun\Cebula3\cebula_react\assets\js\index.js: Support for the experimental syntax 'classProperties' isn't currently enabled (17:9):

  15 | 
  16 | class BodyPartWrapper extends Component {
> 17 |   state = {
     |         ^
  18 | 
  19 |   }
  20 | 

Add @babel/plugin-proposal-class-properties (https://git.io/vb4SL) to the 
'plugins' section of your Babel config to enable transformation.

So, I installed @babel/plugin-proposal-class-properties and put this in babelrc

package.json

{
  "name": "cebula_react",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "webpack-dev-server --config ./webpack.config.js --mode development",
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "webpack --config prod.config.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "babel": {
    "presets": [
      "@babel/preset-env",
      "@babel/preset-react"
    ]
  },
  "devDependencies": {
    "@babel/cli": "^7.0.0",
    "@babel/core": "^7.0.0",
    "@babel/plugin-proposal-class-properties": "^7.0.0",
    "@babel/preset-env": "^7.0.0",
    "@babel/preset-react": "^7.0.0",
    "babel-loader": "^8.0.2",
    "babel-plugin-transform-class-properties": "^6.24.1",
    "react-hot-loader": "^4.3.6",
    "webpack": "^4.17.2",
    "webpack-bundle-tracker": "^0.3.0",
    "webpack-cli": "^3.1.0",
    "webpack-dev-server": "^3.1.8"
  },
  "dependencies": {
    "react": "^16.5.0",
    "react-dom": "^16.5.0"
  }
}

babelrc

{
  "presets": [
    "@babel/preset-env",
    "@babel/preset-react"
  ],
  "plugins": [
    "@babel/plugin-proposal-class-properties"
  ]
}

However the error is still existed, What is the problem??

Change

"plugins": [
    "@babel/plugin-proposal-class-properties"
  ]

To

"plugins": [
    [
      "@babel/plugin-proposal-class-properties",
      {
        "loose": true
      }
    ]
  ]

This worked for me

First install the: @babel/plugin-proposal-class-properties as dev dependency:

npm install @babel/plugin-proposal-class-properties --save-dev

Then edit your .babelrc so it will be exact like this:

{
  "presets": [
      "@babel/preset-env",
      "@babel/preset-react"
  ],
  "plugins": [
      [
        "@babel/plugin-proposal-class-properties"
      ]
  ]
}

.babelrc file located in the root directory, where package.json is.

Note that you should re-start your webpack dev server to changes take affect.