How to make reference in JSON object with in itself to some other key-value pair?

I need to make condition on the next key-value pair regarding to prev key-value value pair existed on json object. And I tried like below -

var json = {'numeric':true,
            'required' : !json.numeric

Of course this doesnot work. I need to write this by two successive steps like below -

var json = {'numeric':true};
json.required = !json.numeric;

Is there any way to acheive first thing.