How do I persuade babel to let me define a Javascript array of consts?

I’m building my first expo/react app. I keep getting an “Unexpected token” error message in App.js:

export default class App extends React.Component {
   const [message, setMessage] = useState("...");

the error being in the [ of the line beginning const.

As best I can tell, this is a babel issue: this syntax was introduced in ES2015. AFAICS, this should be resolvable by adding @babel/preset-env to babel.config.js thus:

module.exports = function(api) {
  api.cache(true);
  return {
      presets: [
          '@babel/react',
          '@babel/env',
      ],
      plugins: [
          '@babel/proposal-class-properties',
      ],
  };
};

Bundling succeeds, but the error remains! What am I missing?