There is why TypeScript IS so great. In the early days of a new app or feature, you have no idea what the correct data/type shapes are. In TypeScript you can

There is why TypeScript IS so great. In the early days of a new app or feature, you have no idea what the correct data/type shapes are. In TypeScript you can define the types and then easily do major refactors even if you have 1000's of lines already written. It becomes so tedious to do the same refactoring in JavaScript. TypeScript makes it trivial to change an object or function signature when developing new code (or old code). Refactors that take 3 minutes in TypeScript take 3 days in JavaScript and you better hope you catch all the uses. The refactor ability that TypeScript gives you makes it so much easier to change data types and function signatures dozens of times until you get things right.