```javascript
const prevMonthFirstDay = moment().subtract(1, 'months').date(1);

const nextMonthLastDay = moment().add(2, 'months').date(0);
```

or

```javascript
const prevMonthFirstDay = moment().subtract(1, 'months').startOf('month');

const nextMonthLastDay = moment().add(1, 'months').endOf('month');
```