if the first term is undefined, isDone will be undefined, not false. At least in Javascript.

&& returns the falsy value on the left side of the expression if it evaluates to a falsy value

(undefined && true) evaluates to undefined

correspondingly || returns the truthy value (which might be an object) on the left hand side if evaluates truthy. That's useful for expressions like this:

const a = b || 'default value';

!! turns truthy/falsy values into booleans.

On top of that, truthy values also propagate, so if isDelivered or isNotified are something else that's truthy (such as a 1 from mysql), isDone will not be True either and risk failing in more interesting ways down the line.