Start of Time1.7.0+

moment().startOf(String);

Mutates the original moment by setting it to the start of a unit of time.

moment().startOf('year');    // set to January 1st, 12:00 am this year
moment().startOf('month');   // set to the first of this month, 12:00 am
moment().startOf('quarter');  // set to the beginning of the current quarter, 1st day of months, 12:00 am
moment().startOf('week');    // set to the first day of this week, 12:00 am
moment().startOf('isoWeek'); // set to the first day of this week according to ISO 8601, 12:00 am
moment().startOf('day');     // set to 12:00 am today
moment().startOf('date');     // set to 12:00 am today
moment().startOf('hour');    // set to now, but with 0 mins, 0 secs, and 0 ms
moment().startOf('minute');  // set to now, but with 0 seconds and 0 milliseconds
moment().startOf('second');  // same as moment().milliseconds(0);

These shortcuts are essentially the same as the following.

moment().startOf('year');
moment().month(0).date(1).hours(0).minutes(0).seconds(0).milliseconds(0);

moment().startOf('hour');
moment().minutes(0).seconds(0).milliseconds(0)

As of version 2.0.0, moment#startOf('day') replaced moment#sod.

Note: moment#startOf('week') was added in version 2.0.0.

As of version 2.1.0, moment#startOf('week') uses the locale aware week start day.

Note: moment#startOf('isoWeek') was added in version 2.2.0.

Note: moment#startOf('date') was added as an alias for day in 2.13.0