JavaScript sorting after concat of two arrays now working

April 13, 2022

I need some help. I’ve used a little function to concat two arrays and remove the duplicates:

let a = ['06.12.2021', '07.12.2021', '19.12.2021', '20.12.2021', '01.03.2022', '03.03.2022', '06.12.2021', '09.01.2022'];
let b = ['17.11.2021', '04.01.2022', '08.01.2022', '09.01.2022'];

let ab = [...new Set( a.concat( b ) )];

console.log(ab);

This works quite nice, but actually they are in a complete bad order. At least, they should start with the lowest date and ends with the highest. I’ve tried a sort function without any success:

let a = ['06.12.2021', '07.12.2021', '19.12.2021', '20.12.2021', '01.03.2022', '03.03.2022', '06.12.2021', '09.01.2022'];
let b = ['17.11.2021', '04.01.2022', '08.01.2022', '09.01.2022'];

let ab = [...new Set(a.concat(b))];

console.log(ab);

ab.sort((a, b) => Date.parse(b) - Date.parse(a));

console.log(ab);

Do you have any advice for me?

>Solution :

I added a custom parse function that transforms your date format dd-MM-yyyy to ISO format yyyy-MM-dd. This fixes the date parse issue. I also changed b - a to a - b which sorts in increasing order.

let a = ['06.12.2021', '07.12.2021', '19.12.2021', '20.12.2021', '01.03.2022', '03.03.2022', '06.12.2021', '09.01.2022'];
let b = ['17.11.2021', '04.01.2022', '08.01.2022', '09.01.2022'];

let ab = [...new Set(a.concat(b))];

console.log(ab);

function parse(date) {
    const [d, m, y] = date.split('.');
    return new Date(y, m-1, d);
}

ab.sort((a, b) => parse(a) - parse(b));

console.log(ab);