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How to Compare Dates in JavaScript

Comparing dates is a fundamental operation in programming, essential for filtering data, validating deadlines, or scheduling events. In JavaScript, this is a straightforward task because Date objects can be compared directly using standard comparison operators like <, >, <=, and >=.

This guide will teach you the core principle of date comparison in JavaScript. You will learn how to check if a date is before, after, equal to, or between other dates, and how to compare a date to the current time to see if it's in the past or future.

The Core Method: Direct Comparison of Date Objects​

JavaScript Date objects can be compared directly because the comparison operators (<, >) implicitly convert the dates to their numeric representation: the timestamp. A timestamp is the number of milliseconds that have elapsed since the Unix Epoch (January 1, 1970, 00:00:00 UTC).

When you write date1 < date2, JavaScript is effectively comparing date1.getTime() < date2.getTime(). This makes date comparisons simple, intuitive, and reliable.

How to Create Date Objects​

To perform a comparison, you must first have valid Date objects.

// From an ISO 8601 string (YYYY-MM-DD) - Recommended
const date1 = new Date('2023-10-27');

// From the current time
const now = new Date();

// From individual components (Year, Month-Index, Day)
// Note: The month is 0-indexed (0 = January, 11 = December)
const date2 = new Date(2024, 0, 1); // January 1, 2024

Basic Examples: Is a Date Before, After, or Equal?​

Let's see the comparison operators in action.

Problem: given two dates, how do we determine their relationship to each other?

// Problem: Compare these two dates.
const d1 = new Date('2023-09-01');
const d2 = new Date('2023-10-27');

Solution:

const d1 = new Date('2023-09-01');
const d2 = new Date('2023-10-27');

// Is d1 before d2?
console.log(d1 < d2);  // Output: true

// Is d1 after d2?
console.log(d1 > d2);  // Output: false

// Are they the same? (Only true if timestamps are identical)
const d3 = new Date('2023-09-01');
console.log(d1.getTime() === d3.getTime()); // Output: true

Practical Use Cases​

With this basic principle, we can solve several common problems.

How to Check if a Date is in the Past​

To check if a date is in the past, simply compare it to the current date and time.

function isInThePast(date) {
  const now = new Date();
  return date < now;
}

// Example Usage:
const yesterday = new Date();
yesterday.setDate(yesterday.getDate() - 1);

console.log(isInThePast(yesterday)); // Output: true
console.log(isInThePast(new Date('2099-01-01'))); // Output: false

How to Check if a Date is in the Future​

To check if a date is in the future, you do the opposite comparison.

function isInTheFuture(date) {
  const now = new Date();
  return date > now;
}

// Example Usage:
const tomorrow = new Date();
tomorrow.setDate(tomorrow.getDate() + 1);

console.log(isInTheFuture(tomorrow)); // Output: true
console.log(isInTheFuture(new Date('2000-01-01'))); // Output: false

How to Check if a Date is Between Two Other Dates​

To check if a date falls within a range, you perform two comparisons.

function isBetween(date, start, end) {
  return date >= start && date <= end;
}

// Example Usage:
const eventDate = new Date('2023-10-27');
const startDate = new Date('2023-10-01');
const endDate = new Date('2023-10-31');

console.log(isBetween(eventDate, startDate, endDate)); // Output: true

Important Note: Comparing by "Day" vs. "Time"​

A common "gotcha" is that date comparisons are precise down to the millisecond. If you want to check if a date is "yesterday or earlier," you need to be careful with the current time.

Problem: a date of 2023-10-26T23:00 is technically before 2023-10-27T10:00 (today at 10 AM). But if you only care about the calendar day, this can cause issues.

Solution: to compare by day only, set the time component of both dates to midnight (00:00:00.000) before comparing.

function isBeforeToday(date) {
  const today = new Date();
  // Set the time of "today" to the very beginning of the day.
  today.setHours(0, 0, 0, 0);

  // Now the comparison is based purely on the calendar date.
  return date < today;
}

const lastNight = new Date(); // e.g., '2023-10-26T23:00'
lastNight.setHours(lastNight.getHours() - 12);

const yesterday = new Date(); // e.g., '2023-10-26T10:00'
yesterday.setDate(yesterday.getDate() - 1);

console.log(isBeforeToday(lastNight)); // Output: false
console.log(isBeforeToday(yesterday)); // Output: true
note

This technique ensures your comparisons are "day-based" rather than "time-based," which is often the desired logic for user-facing applications.

Conclusion​

Comparing dates in JavaScript is a simple and powerful feature once you understand the underlying principle.

  • Date objects can be compared directly using standard operators (<, >, <=, >=) because they are converted to numeric timestamps.
  • To check if a date is in the past or future, simply compare it to a new Date() object.
  • For comparisons that should only consider the calendar day, remember to normalize the time part of your dates by setting the hours, minutes, and seconds to 0 with date.setHours(0, 0, 0, 0).

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