The comma operator can lead to excessively tricky expressions. It can also mask some programming errors.
JSLint expects to see the comma used as a separator, but not as an operator
(except in the initialization and incrementation parts of the
for statement). It does not expect to see elided
elements in array literals. Extra commas should not be used. A comma should not
appear after the last element of an array literal or object literal because it can
be misinterpreted by some browsers.