javascript - How to get list of days in a month with Moment.js

Question

Using Moment.js I would like to get all days in a month of specific year in an array. For example:

January-2014:
[
"01-wed",
"02-thr",
"03-fri",
"04-sat"
]

any suggestions? I looked through Moment.js docs but couldn't find anything. The closet I got was this:

moment("2012-02", "YYYY-MM").daysInMonth() 

But this only return an int with total days for specific month not an array with each day.

Answer 1

Here's a function that will do the trick (not using Moment, but just vanilla JavaScript):

var getDaysArray = function(year, month) {
  var monthIndex = month - 1; // 0..11 instead of 1..12
  var names = [ 'sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat' ];
  var date = new Date(year, monthIndex, 1);
  var result = [];
  while (date.getMonth() == monthIndex) {
    result.push(date.getDate() + '-' + names[date.getDay()]);
    date.setDate(date.getDate() + 1);
  }
  return result;
}

For example:

js> getDaysArray(2012,2)
["1-wed", "2-thu", "3-fri", "4-sat", "5-sun", "6-mon", "7-tue",
 "8-wed", "9-thu", "10-fri", "11-sat", "12-sun", "13-mon", "14-tue",
"15-wed", "16-thu", "17-fri", "18-sat", "19-sun", "20-mon", "21-tue", 
"22-wed", "23-thu", "24-fri", "25-sat", "26-sun", "27-mon", "28-tue",
"29-wed"]

ES2015+ version - also hid the array of names behind a closure so it's only initialized once:

const getDaysArray = (function() {
  const names = Object.freeze([ 'sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat' ]);
  return (year, month) => {
    const monthIndex = month - 1
    const date = new Date(year, monthIndex, 1);
    const result = [];
    while (date.getMonth() == monthIndex) {
      result.push(`${date.getDate()}-${names[date.getDay()]}`);
    date.setDate(date.getDate() + 1);
    }
    return result;
  }
})();

As a side note, you can see that declaring the date const doesn't keep us from mutating it (nor would Object.freeze, used to make the weekday names array immutable, do anything to a Date). We're taking advantage of the mutability here, but if we actually wanted an immutable Date with the language enforcing that immutability in current Javascript, we'd have to go to some length.

Also note that the solutions above don't zero-pad dates before the 10th, unlike the sample output included in the question. With ES2017+ that's pretty easy to fix:

    result.push(`${date.getDate()}`.padStart(2,'0') + `-${names[date.getDay()]}`);

Doing it in older versions of JS requires rolling your own zero-padding logic, which isn't hard but is also not really the focus of the question.