TypeScript is a good solution for this. I use ES2015+ features this way regularly and they perform great. I target ES5 so they are transpiled at build time, and

TypeScript is a good solution for this. I use ES2015+ features this way regularly and they perform great. I target ES5 so they are transpiled at build time, and as an added bonus I get async/await which is seriously a life saver in certain situations. Edit... I work at Microsoft (I'm supposed to disclose this), but not on the TypeScript team.