JavaScript: Programmatically Determine the Upcoming Decade's End

1. Extracting the Year
   It might first extract the year part from the provided date object.
2. Decade Calculation
   Then, it would calculate the decade by subtracting the remainder of dividing the year by 10 from the year itself. For instance, for 2023, it would be 2023 - (2023 % 10) = 2020.
3. Setting the Date
   Finally, it would create a new date object by setting the year to the end of the decade (which is the calculated decade plus 9), and setting the month and day to December 31st (assuming the end of the decade is desired).

For example, if you provide endOfDecade(new Date(2023, 5, 15)), it might return a date object representing December 31st, 2029 (assuming a base date like January 1st, 1970 is used for calculations).

Here are some resources that might be helpful:

• Specific documentation on endOfDecade might be available on the date-fns website or npm package documentation. You can search for it online.

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import { endOfDecade } from 'date-fns';

const today = new Date();
const endOfCurrentDecade = endOfDecade(today);

console.log(endOfCurrentDecade); // This will output a Date object representing the end of the current decade.

This code first imports the endOfDecade function from date-fns. Then, it creates a Date object representing today's date. Finally, it calls endOfDecade with today's date and stores the result in a variable endOfCurrentDecade. This variable will hold a Date object representing the end of the decade that today falls within.

Note
Make sure you have date-fns installed in your project before running this code. You can install it using npm or yarn:

npm install date-fns

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Manual Calculation

function endOfDecade(date) {
  const year = date.getFullYear();
  const decade = Math.floor(year / 10) * 10;
  return new Date(decade, 11, 31); // Set month to December (11) and day to 31st
}

const today = new Date();
const endOfCurrentDecade = endOfDecade(today);

console.log(endOfCurrentDecade);

This code defines a function endOfDecade that takes a date as input. It calculates the decade by dividing the year by 10 and multiplying by 10 again to get the starting year. Finally, it creates a new Date object for December 31st of that decade.

Using Other date-fns Functions

import { setYear, addYears, lastDayOfMonth } from 'date-fns';

const today = new Date();
const year = today.getFullYear();
const decade = Math.floor(year / 10) * 10;
const endOfDecade = lastDayOfMonth(setYear(addYears(today, 9 - (year % 10)), decade));

console.log(endOfDecade);

This code first calculates the decade similar to the previous approach. Then it uses addYears to add 9 years to get to the end of the decade. It subtracts the remainder of dividing the year by 10 to account for the current year's position within the decade. Finally, it uses setYear to set the year to the calculated decade and lastDayOfMonth to get the last day of December (31st).

Both approaches achieve the same functionality as a potential endOfDecade function. Choose the one that best suits your project's needs and coding style.