How to enable support for the experimental syntax 'classPrivateProperties'?

Question

I am getting the following error in my React project when trying to import ethers:

./node_modules/ethers/lib.esm/abi/abi-coder.js
SyntaxError: /node_modules/ethers/lib.esm/abi/abi-coder.js: Support for the experimental syntax 'classPrivateProperties' isn't currently enabled (107:5)

How can I enable support for the experimental syntax classPrivateProperties?

My package.json looks like this:

{
  "name": "bradshawknox",
  "description": "A simple manage plan app powered by Stacks.js",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@blockstack/ui": "^2.12.14",
    "@coreui/react": "^4.5.2",
    "@emotion/core": "^11.0.0",
    "@emotion/css": "^11.0.0",
    "@emotion/react": "^11.10.5",
    "@emotion/styled": "^11.10.5",
    "@mui/material": "^5.11.8",
    "@reduxjs/toolkit": "^1.5.1",
    "@stacks/connect": "^4.3.18",
    "@stacks/storage": "^1.3.3",
    "@walletconnect/web3-provider": "^1.8.0",
    "axios": "^0.21.1",
    "blockstack": "^19.3.0",
    "ckeditor4-react": "^1.4.1",
    "ckeditor5-custom-build": "file:./ckeditor5",
    "emailjs-com": "^2.6.4",
    "ethers": "^6.0.2",
    "export-from-json": "^1.3.4",
    "file-saver": "^2.0.5",
    "firebase": "^8.4.1",
    "html2canvas": "^1.0.0-rc.7",
    "jquery": "^3.6.0",
    "jspdf": "^2.3.1",
    "lodash": "^4.17.21",
    "moment": "^2.29.1",
    "ra-data-simple-rest": "^3.13.4",
    "radiks": "^0.2.2-beta.1",
    "react": "^16.13.1",
    "react-admin": "^3.15.1",
    "react-bootstrap": "^1.6.0",
    "react-bootstrap-sweetalert": "^5.2.0",
    "react-dark-mode-toggle": "^0.2.0",
    "react-datepicker": "^3.8.0",
    "react-dom": "^16.13.1",
    "react-firebase-hooks": "^3.0.3",
    "react-google-recaptcha": "^2.1.0",
    "react-loadingg": "^1.7.2",
    "react-recaptcha": "^2.3.10",
    "react-recaptcha-google": "^1.1.1",
    "react-redux": "^7.2.3",
    "react-router-dom": "^5.2.0",
    "react-scripts": "^3.4.1",
    "react-spinners": "^0.10.6",
    "react-table-v6": "^6.8.6",
    "react-toast-notifications": "^2.4.3",
    "reactstrap": "^9.1.5",
    "redux": "^4.0.5",
    "redux-persist": "^6.0.0",
    "request": "^2.88.2",
    "request-promise": "^4.2.6",
    "styled-components": "^5.2.1",
    "use-dark-mode": "^2.3.1",
    "uuid": "^8.1.0"
  },
  "prettier": "@blockstack/prettier-config",
  "scripts": {
    "start": "react-app-rewired start",
    "build": "react-app-rewired build",
    "test": "react-app-rewired test --env=jsdom",
    "eject": "react-app-rewired eject",
    "lint": "eslint src/**/*.{js,jsx}",
    "lint:fix": "eslint src/**/*.{jsx,js} --fix"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "devDependencies": {
    "@blockstack/eslint-config": "^1.0.5",
    "@blockstack/prettier-config": "0.0.6",
    "enzyme": "^3.10.0",
    "enzyme-adapter-react-16": "^1.14.0",
    "eslint-config-react-app": "^5.2.1",
    "react-addons-test-utils": "^15.6.2",
    "react-app-rewired": "^2.0.1"
  },
  "proxy": "http://localhost:2000"
}

Answer 1

To enable support for the experimental syntax classPrivateProperties you have to use babel in your project:

1. Add devDependencies by running:

npm i @babel/preset-env @babel/preset-react @babel/plugin-proposal-class-properties --save-dev

2. Create .babelrc file in your root folder with the following content:

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