>Typescript combines typing and transpilation together, essentially doing what flow+Babel does. Typescript allows you use newer JS features like Babel but produ

>Typescript combines typing and transpilation together, essentially doing what flow+Babel does. Typescript allows you use newer JS features like Babel but produces much cleaner JavaScript. It's important to keep in mind that the simplicity of TS's ES5 codegen comes with the tradeoff that it isn't spec-compliant. For example, given a program `for (const el of arr) { }`, TS's codegen is a loop like `for(var i = 0; i < arr.length; i++) { var el = arr[i]; }` whereas Babel's codegen uses `Symbol.iterator`. The former is technically wrong in an environment where `arr` happens to have a custom `[Symbol.iterator]`. Another example is ES2015 classes, for which Babel's codegen asserts the constructor is being called with `new` whereas TS's doesn't.