Operators in Javascript

| This operation starts with a meaningful return. Otherwise, the last expression is returned (not necessarily a Boolean value );

& The operation is like this: starting from the first, a meaningless return is returned; otherwise, the last expression is returned (same as above );

! The operation is as follows: Take the non-value of the expression (note that it is not for the expression ).

What is meaningless? The following six values are 0, null, undefined, "", false, and Nan. This makes sense.