How to get relative date from now using date.js Jquery

I'm looking for an 'elegant' solution to get the number of the days between a specific date and now.

I manipulate dates using date.js, and I prefer to use date.js in the solution.

function relatedDays(relatedDate){

var diff= Date.today()-relatedDate;

return ???

}

var tomorrow=Date.today().addDays(1);

relateDays(tomorrow); // result : 1