// source
for await (const x of y) {
  ...
}

// output
var _done, _value, _errorFromLoopBody, _returnFunction, _result;
try {
    var _nonUserCode = true; // start non-user code section
    for (var _iter = y[Symbol.asyncIterator](); _result = await _iter.next(), _done = _result.done, !_done;) {
        _value = _result.value;
        _nonUserCode = false; // end non-user code
        // start user code
        try {
            const x = _value;
            ...
        }
        finally {
            // end user code
            _nonUserCode = true; // start non-user code
        }
    }
}
catch (error) {
    _errorFromLoopBody = { error };
}
finally {
    try {
        // only call return if abruptly exiting from _user_ code.
        if (!_nonUserCode && !_done && (_returnFunction = _iter.return)) {
            yield _returnFunction.call(_iter);
        }
    }
    finally {
        if (_errorFromLoopBody) throw _errorFromLoopBody.error;
    }
}
// end non-user code