TypeScript and Flow have the same behavior with regard to removing types, and TypeScript and Babel have the same behavior with regard to downleveling ES6+ code

TypeScript and Flow have the same behavior with regard to removing types, and TypeScript and Babel have the same behavior with regard to downleveling ES6+ code to ES5- If you target ES6 with TypeScript and only write ES6-compliant code (plus types), you won't get any downleveling of features, so your code will always be the same as you wrote it (other than the removal of types). If you use TS-specific features like 'enum' or 'namespace', there will necessarily be some rewriting of your code to turn it into usable JS, but those features are entirely optional.