javascript: разница между датами

var time_from=new Date(order_from['y'],order_from['m']-1,order_from['d']);
var time_to=new Date(order_to['y'],order_to['m']-1,order_to['d']);
var order_days=Math.floor((time_to.getTime()-time_from.getTime())/(1000*60*60*24));