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.

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.