How to Sort array of objects by a property value

Question

I have an array of objects like this. I am trying to sort the array if the holidays have the same holiday_on, and Sort by holiday_for By Descending Order.

const holidays: IHoliday[] = [
    {
        id: 1,
        holiday_for: 1,
        holiday_on: "2021-10-26"
    },
    {
        id: 2,
        holiday_for: 3,
        holiday_on: "2021-10-26"
    },
    {
        id: 3,
        holiday_for: 1,
        holiday_on: "2021-11-26"
    },
    {
        id: 4,
        holiday_for: 3,
        holiday_on: "2021-11-26"
    },
    {
        id: 5,
        holiday_for: 4,
        holiday_on: "2021-11-26"
    }
]

With the implementation below getting this type error Argument of type '(a: IHoliday, b: IHoliday) => number | undefined' is not assignable to parameter of type '(a: IHoliday, b: IHoliday) => number'.Type 'number | undefined' is not assignable to type 'number'

If I make the holidays array any type then typescript giving another warning - Not all code paths return a value.

Implementation

const sorted = holidays.sort((a: IHoliday, b: IHoliday) => {
    if (a.holiday_on === b.holiday_on) {
        return b.holiday_for - a.holiday_for;
    }
});

Does this answer your question? Sort array of objects by string property value — msanford
– msanford, Commented Sep 17, 2021 at 3:04
I would suggest to use a library underscore or lodash both the libraries have lot of inbuilt utilities — lakshmi narayana
– lakshmi narayana, Commented Sep 17, 2021 at 4:55

dom.macs · Accepted Answer · 2021-09-17 03:38:38Z

I added another return so that if the holiday_on is not the same, it will sort the date but you cannot directly make an operation with the type Date in Typescript. Using getTime() method converts a Date into a number (Date.prototype.getTime()) so you can make the operation without error.

const sorted = this.holidays.sort((a: IHoliday, b: IHoliday) => {
  if (a.holiday_on === b.holiday_on) {
    return b.holiday_for - a.holiday_for;
  }
  return (
    new Date(b.holiday_on).getTime() - new Date(a.holiday_on).getTime()
  );
});
console.log(sorted);

I added a stackblitz for you to play on.

aelesia · Accepted Answer · 2021-09-17 02:56:40Z

0

Your sort function needs to always return a number. 0 if equal, >=1 if greater, and <=-1 if smaller.

const sorted = holidays.sort((a: IHoliday, b: IHoliday) => {
    if (a.holiday_on === b.holiday_on) {
        return b.holiday_for - a.holiday_for;
    }
    return new Date(b.holiday_on) - new Date(a.holiday_on)
});

This function will attempt to sort by holiday_on first, and only if it's equal, then it sorts by holiday_for.

answered Sep 17, 2021 at 2:56

aelesia

1929 bronze badges

2 Comments

RAHUL KUNDU Over a year ago

In the second return where you have added new Date getting this error - The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

aelesia Over a year ago

Code should work if you ignore the error, but to be more specific you can use return new Date(b.holiday_on).getTime() - new Date(a.holiday_on).getTime()

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