Why does Javascript (ES.next) force me to declare a function as async if I want to use await? -

it seems compiler / parser should smart enough detect if function uses await automatically becomes async function.

why forced type async keyword? adds clutter , there many times forget add , error , have go , add it.

would there disadvantage having compiler automatically promote function async when sees await , save hassle of dealing it?

compare async functions es6 generator functions , pretty obvious:

function* x() {} // generator function without 'yield' object.getprototypeof(x); // returns generatorfunction 

generator functions inherently different traditional functions, not need have yield expression in body. there a bug in es6 proposal stated syntax error if generator function not contain yield, fixed:

one important use case prototyping dummy generator. or case comment out yield debugging. shouldn't render program illegal.

the same holds async functions: according the draft, async function not required have awaits in body while still behaving different traditional function.

let's comment await out. should interpreter parse async function traditional function , possibly break whole code? better not.