Basic features and some ES6 doesn't work.

I would really like if we could use all of this in our Khan Academy code:
```
function f() { // Very basic. Yet Oh Noes prefers us writing it the messier way.
}
async function getButtonPressed() { // No, I didn't mean to type "asin", Oh Noes.
return (await buttonClickedPromise).name;
}
class HowAboutThis { // It would also be nice if we could do elegant classes like this.
constructor(x) {
this.x = x;
}
}
let thisDoesntWork = true;
const neitherDoesThis = true;

square = x => x * x; // Arrow functions would also be good

let enhancedObjectLiteral = {
value: 3,
square, // Easy shorthand for square: square,
getDoubleValue() { return value * 2; } // Easy methods read like functions
};

function defaultParametersAreVeryUseful(a, isCorrect=true, b, c) {}
function restParametersAreBetterThanArgumentsList(a, b, ...rest) {}

for (let x of iterable) {
// much better than "for (var i = 0; i < iterable.length; i++) { iterable[i] }
}

function * getPositiveIntegers(x=0) {
yield x + 1;
}

// Thanks for your consideration. Teaching new programmers ES6 features will not only help their code be better, it will make sure they are up to date with modern JavaScript when they eventually get a job.
```

No files, tests, or entry points are named in the issue. Start by locating the live editor's JavaScript parsing or execution entry points and determine which listed ES6 constructs are unsupported; done means the requested syntax works in Khan Academy code.

Written by the indexing model from the issue text.