lib/messageformat.d.ts uses export default, but lib/messageformat.js file uses module.exports = MessageFormat. This will cause TypeScript under the node16 module mode to think an extra .default property access is required, but that will likely fail at runtime. These types should use export = MessageFormat instead of export default.

See https://arethetypeswrong.github.io/?p=%40messageformat%2Fcore%403.4.0