How do I find the nearest Past or Future Date in an array of Dates by an DateObject?

Let’s say we have an Array of Dates

var dateArr = [new Date("Thu Apr 01 2021 00:00:00 GMT+0200"), new Date("Sat May 01 2021 00:00:00 GMT+0200")];

and an Date Object, which we need to search in the dateArr, for example:

var findDate = new Date("Mon Apr 05 2021 07:50:06 GMT+0200");

And all together we have this PLUS

• a function to return us the nearestDate in dateArr by findDate which can lie in the past or future

var dateArr = [new Date("Thu Apr 01 2021 00:00:00 GMT+0200"), new Date("Sat May 01 2021 00:00:00 GMT+0200")];

var findDate = new Date("Mon Apr 05 2021 07:50:06 GMT+0200");

var result = getNearestDateInDateArrByFindDate(dateArr, findDate);

console.log(result); //should print to console: Thu Apr 01 2021 00:00:00 GMT+0200

function getNearestDateInDateArrByFindDate(dateArr, findDate) {
   var nearestDateInPastOrFuture;

   ...

   return nearestDateInPastOrFuture;
}

What I tried so far without sucess …

var dateArr = [new Date("Thu Apr 01 2021 00:00:00 GMT+0200"), new Date("Sat May 01 2021 00:00:00 GMT+0200")];

var findDate = new Date("Mon Apr 05 2021 07:50:06 GMT+0200");

function getNearestDateInDateArrByFindDate(dateArr, findDate) {

        console.log(dateArr);
        console.log(findDate);

        var nearestFutureDates = dateArr.filter(dt => dt.getTime() >= findDate.getTime());
        var nearestFutureDates = nearestFutureDates.sort((a, b) => a.getTime() - b.getTime());

        var nearestPastOrFutureDate = dateArr.filter(dt => dt.getTime() >= findDate.getTime());
        var nearestPastOrFutureDate = nearestPastOrFutureDate.sort((a, b) => (findDate.getTime() - a.getTime()) - (findDate.getTime() - b.getTime()));

        console.log(nearestFutureDates);
        console.log(nearestPastOrFutureDate);
  //returns always sat May 01 2021 00:00:00 GMT+0200
}


getNearestDateInDateArrByFindDate(dateArr, findDate)

And somehow the snippet doesn’t return Apr 01 but rather April 31?

Answer

We can use Array.sort() to sort by the difference in ms from each date to findDate.

NB: We can get the absolute difference in milliseconds between two dates using

Math.abs(date1 - date2);

So we’ll use this to sort like so:

var dateArr = [new Date("Thu Apr 01 2021 00:00:00 GMT+0200"), new Date("Sat May 01 2021 00:00:00 GMT+0200")];

var findDate = new Date("Mon Apr 05 2021 07:50:06 GMT+0200");

var result = getNearestDateInDateArrByFindDate(dateArr, findDate);

console.log(result); //should print to console: Thu Apr 01 2021 00:00:00 GMT+0200

function getNearestDateInDateArrByFindDate(dateArr, findDate) {
    const sortedByDiff = [...dateArr].sort((a,b) => {
        // Sort by the absolute difference in ms between dates.
        return Math.abs(a - findDate) - Math.abs(b - findDate);
    })
    // Return the first date (the one with the smallest difference)
    return sortedByDiff[0];
}