How to sort an array of events by month in JavaScript?

Question

How could I sort an array of events by the month they are occuring in?

For instance, I want to sort this events array:

[{ event: 'prom', month: 'MAY' },
 { event: 'graduation', month: 'JUN' },
 { event: 'dance', month: 'JAN' }]

to become this array:

[{ event: 'dance', month: 'JAN' },
{ event: 'prom', month: 'MAY' },
{ event: 'graduation', month: 'JUN' }]

An array of MONTHS is also provided:

const MONTHS = [
    'JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN',
    'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC'
];

I'm trying to sort the events array using the sort method, but it is only sorting in alphabetical order. Could anyone help give me guidance to figure out how I can sort by the calendar order of months?


const MONTHS = [
    'JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN',
    'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC'
];


function sortByMonth(events) {
    events.sort((a,b) => 
        a.month.localeCompare(b.month)
    )
}

Nina Scholz · Accepted Answer · 2022-11-25T19:10:34.860

You could sort by the indices of the months.

const
    MONTHS = ['JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN', 'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC'],
    events = [{ event: 'prom', month: 'MAY' }, { event: 'graduation', month: 'JUN' }, { event: 'dance', month: 'JAN' }];

events.sort((a, b) => MONTHS.indexOf(a.month) - MONTHS.indexOf(b.month));

console.log(events);

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If you have sometime no month property or a value different of the given months, you could add a default value for moving this item to top (0) or bottem (Number.MAX_VALUEor a larger value than the length of the array).

const
    MONTHS = ['JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN', 'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC'],
    events = [{ event: 'prom', month: 'MAY' }, { event: 'party', month: '' }, { event: 'graduation', month: 'JUN' }, { event: 'dance', month: 'JAN' }];

events.sort((a, b) =>
    (MONTHS.indexOf(a.month) + 1 || Number.MAX_VALUE) -
    (MONTHS.indexOf(b.month) + 1 || Number.MAX_VALUE)
);

console.log(events);

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score 1 · Answer 2 · answered Nov 25 '22 at 19:03

Using Array#indexOf:

const
  arr = [ { event: 'prom', month: 'MAY' }, { event: 'graduation', month: 'JUN' }, { event: 'dance', month: 'JAN' } ],
  MONTHS = [ 'JAN', 'FEB', 'MAR', 'APR', 'MAY', 'JUN', 'JUL', 'AUG', 'SEP', 'OCT', 'NOV', 'DEC' ];

arr.sort((a, b) => MONTHS.indexOf(a.month) - MONTHS.indexOf(b.month));

console.log(arr);

How to sort an array of events by month in JavaScript?

2 Answers2