JSFiddle - React, Tailwind, and code Playground

JavaScript

flatMapPolyfill = (ArrayConstructor = Array) => {
  Object.defineProperty(ArrayConstructor.prototype, 'flatMap', {
    configurable: true,
    enumerable: false,
    writable: true,
    value: function flatMap(callback) {
      return ArrayConstructor.map(callback).flat(1);
    }
  });
};