`.toExponential()` outputting different value from `.toNumber()`

[KurtPreston]

In this example, I add 0.1 + 0.2.

.toNumber() correctly returns 0.3.
However, .toExponential() returns 3154074395550978868244478235406793e-1

import {Double} from 'double.js/dist/double.esm.js';

const pointThree = new Double('0.1').add(new Double('0.2'));
console.log('pointThree.toNumber(): ', pointThree.toNumber()); // 0.3
console.log('pointThree.toExponential(): ', pointThree.toExponential()); // 3154074395550978868244478235406793e-1