Yes, there's a note right after: Note that this trick should only be used for arrays which you know do not contain "falsy" values (arrays of objec

Yes, there's a note right after: Note that this trick should only be used for arrays which you know do not contain "falsy" values (arrays of objects or DOM nodes for example). If you are iterating over numeric data that might include a 0 or string data that might include the empty string you should use the i, len idiom instead.