Question

Should we write

var a = [ 'a', 'b', 'c', ];
var b = { '1', '2', '3', };

or

var a = [ 'a', 'b', 'c' ];
var b = { '1', '2', '3' };

What is the most correct way?

I’ve noticed that old versions of IE raise error if there is comma expecting there would be a another array item (or property) after comma.

Answer 1

I’ve noticed that old versions of IE raise error if there is comma

That is reason enough to not put a comma after the last element! However, it is valid to do so.

Note however that your 2nd example…

var b = { '1', '2', '3', };

…will throw a syntax error. I’m guessing you intended to make it an object literal, but just made a mistake when writing the question:

var b = { x: '1', y: '2', z: '3', }; //Object literal, no syntax error :)