Sort array of objects by single key with date value

javascript

date-sorting

performance-optimization

javascript-best-practices

byNikita Barsukov·Jan 5, 2025

To sort an array of objects using JavaScript, we typically leverage the sort() method, comparing Date objects that are created from date strings for accurate sorting.

const array = [{ dateKey: '2021-01-01' }, { dateKey: '2020-01-01' }];
array.sort((a, b) => new Date(a.dateKey) - new Date(b.dateKey));

This above code sorts the array in ascending order. Swap a and b to sort in descending order.

Unraveling the time-space continuum or date sorting

Date sorting in JavaScript may seem as natural as breathing, but there are subtle complexities, like date formats and time zones. Performance consideration also comes into play when we deal with large datasets.

Date formats: Normalize don't Mesmerize

Although Date object in JavaScript bravely digests a swath of date string formats, it's advisable to use an incontestable format such as ISO 8601 (YYYY-MM-DD).

// Preferred ISO 8601 Date format
const array = [{ dateKey: '2021-01-01T00:00:00Z' }, { dateKey: '2020-01-01T00:00:00Z' }];

In a wild scenario where dates are not ISO formatted or use different formats, normalizing them can save you a heck of a time.

Time zones and DST: A Gordian Knot

Handling time zones and Daylight Saving Time (DST) without tearing apart the fabric of space-time can be challenging. Always adopt UTC dates and times to brave these cosmic disturbances.

// Converting to UTC before sorting
array.sort((a, b) => 
  new Date(a.dateKey).getTime() - new Date(b.dateKey).getTime());

Above code relies on Unix timestamp. Note that Unix doesn't care for earthly time constructs like time zones.

Large datasets: Dance with Performance

Array.sort() method sorts in place, saving memory but gets sluggish for large arrays. External libraries like lodash or underscore can leap over this performance barrier with grace.

// Lodash's sortBy function doing the heavy lift
const sortedArray = _.sortBy(array, (element) =>
  new Date(element.dateKey).getTime());

Immutable sort: Preserve, Prevent

For cases demanding an immutable sort to leave the original array untouched, spread operator ... or immutable specific libraries are your best allies.

// Spread operator ensures the original array takes no arrow to the knee
const sortedArray = [...array].sort((a, b) => 
  new Date(a.dateKey) - new Date(b.dateKey));

Code readability: Your Future Self Thanks You

ES6 arrow functions can concoct your sorting function into something sweet and petite. Celebrate clean, maintainable code.

// Cleaner arrow function syntax
array.sort((a, b) => +new Date(a.dateKey) - +new Date(b.dateKey));
// Plus operator (+) in front of new Date to ensure comparator returns a number.

Browser compatibility: Time Travel to Past

Beware that the old realm of browser environments may not be ready for ES6. To ensure compatibility with the old worlds, call upon the powers of Babel to transpile your ES6 script into the good old ES5.

Practical Scenarios and Solutions

Whether your array contains date strings in varying formats, or you want to optimize sorting with higher-order functions, or you're working with different locales - these methods are your trusty companions.

My date has many masks

Harmonize date formats before you delve into sorting when your array dance in different date masks.

Higher-order Functions: More Power to You

In advanced scenarios, like when ordering first by date, then by another attribute like ID or name, leverage higher-order functions to gain greater control over sorting logic.