Supported features

Feature	Language Version	Support
ES3 keywords as identifiers	ES5	yes
getters & setters	ES5	Yes, but cannot be transpiled down to ES3. Negatively impact optimizations.
reserved words as properties	ES5	yes
string continuation	ES5	yes
trailing comma	ES5	yes
arrow function	ES6	yes
binary literal	ES6	yes
octal literal	ES6	yes
block-scoped function declaration	ES6	yes
class	ES6	yes
class extends	ES6	yes
class getters / setters	ES6	Yes, but cannot be transpiled down to ES3. Negatively impact optimizations.
computed properties	ES6	yes
const declaration	ES6	yes
let declaration	ES6	yes
default parameter	ES6	yes
rest parameter	ES6	yes
array destructuring	ES6	yes
array pattern rest	ES6	yes
object destructuring	ES6	yes
extended object literal	ES6	yes
member declaration	ES6	yes
for-of loop	ES6	yes
generators	ES6	yes
new.target	ES6	yes
RegExp flag 'u'	ES6	recognized in input, but cannot be transpiled
RegExp flag 'y'	ES6	recognized in input, but cannot be transpiled
string template literals	ES6	yes
ES modules	ES6	yes in input, but output is one large script, possibly broken into chunks
exponent operators	ES7	yes
async functions	ES8	yes
trailing comma in param list	ES9	yes
spread into object literal	ES_2018	yes
object pattern rest	ES_2018	yes
async generator functions	ES_2018	yes
for-await-of loop	ES_2018	yes
RegExp flag 's'	ES_2018	recognized in input, but cannot be transpiled
RegExp lookbehind	ES_2019	recognized in input, but cannot be transpiled
RegExp named groups	ES_2018	recognized in input, but cannot be transpiled
RegExp unicode property escape	ES_2018	yes
Unescaped Unicode line or paragraph separator	ES_2019	yes
Optional catch binding	ES_2019	yes
Dynamic module import	ES_UNSUPPORTED	recognized in input, but cannot be output or transpiled
import.meta	ES_NEXT	recognized in input, but cannot be output or transpiled
Nullish coalescing operator ??	ES_UNSUPPORTED	work in progress
Optional chaining operator ?.	none	work to start soon