If you are using moment.js you can do it easily.
var start = moment("2018-03-10", "YYYY-MM-DD");
var end = moment("2018-03-15", "YYYY-MM-DD");
//Difference in number of days
moment.duration(start.diff(end)).asDays();
//Difference in number of weeks
moment.duration(start.diff(end)).asWeeks();
If you want to find difference between a given date and current date in number of days (ignoring time), make sure to remove time from moment object of current date as below
moment().startOf('day')
To find difference between a given date and current date in number of days
var given = moment("2018-03-10", "YYYY-MM-DD");
var current = moment().startOf('day');
//Difference in number of days
moment.duration(given.diff(current)).asDays();