js get difference in days

1const date1 = new Date('7/13/2010');
2const date2 = new Date('12/15/2010');
3console.log(getDifferenceInDays(date1, date2));
4console.log(getDifferenceInHours(date1, date2));
5console.log(getDifferenceInMinutes(date1, date2));
6console.log(getDifferenceInSeconds(date1, date2));
7
8function getDifferenceInDays(date1, date2) {
9  const diffInMs = Math.abs(date2 - date1);
10  return diffInMs / (1000 * 60 * 60 * 24);
11}
12
13function getDifferenceInHours(date1, date2) {
14  const diffInMs = Math.abs(date2 - date1);
15  return diffInMs / (1000 * 60 * 60);
16}
17
18function getDifferenceInMinutes(date1, date2) {
19  const diffInMs = Math.abs(date2 - date1);
20  return diffInMs / (1000 * 60);
21}
22
23function getDifferenceInSeconds(date1, date2) {
24  const diffInMs = Math.abs(date2 - date1);
25  return diffInMs / 1000;
26}

1let today = new Date().toISOString().slice(0, 10)
2
3const startDate  = '2021-04-15';
4const endDate    = today;
5
6const diffInMs   = new Date(endDate) - new Date(startDate)
7const diffInDays = diffInMs / (1000 * 60 * 60 * 24);
8
9
10alert( diffInDays  );

1const diffDays = (date, otherDate) => Math.ceil(Math.abs(date - otherDate) / (1000 * 60 * 60 * 24));
2
3// Example
4diffDays(new Date('2014-12-19'), new Date('2020-01-01'));   // 1839

1function javascript (date1, date2) {
2   let oned = 24 * 60 * 60 * 1000;
3   return Math.ceil((date2 - date1) / oned);
4}
5
6function javascript(date1, date2) {
7	return new Date(date2 - date1).getDate() - 1
8}
9
10function javascript(date1, date2) {
11  return Math.ceil((date2 - date1) / 8.64e7);
12}

1const date1 = new Date('19/1/2021');
2const date2 = new Date('20/1/2021');
3const diffTime = Math.abs(date2 - date1);
4const diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24)); 
5console.log(diffTime + " milliseconds");
6console.log(diffDays + " days");