Chapter 1.1: Comparing Timestamps

A straightforward approach to comparing two dates involves examining their timestamps. You can obtain a date's timestamp using the getTime method. Here's an example:

const d1 = new Date();

const d2 = new Date(d1);

const same = d1.getTime() === d2.getTime();

const notSame = d1.getTime() !== d2.getTime();

The getTime method returns the number of milliseconds since January 1, 1970, at midnight UTC. Alternatively, you can simplify this by using the unary + operator:

const d1 = new Date();

const d2 = new Date(d1);

const same = +d1 === +d2;

const notSame = +d1 !== +d2;

This expression functions similarly to getTime.

Chapter 1.2: Utilizing Relational Operators

You can also use relational operators directly with date objects for comparison:

const d1 = new Date(2021, 0, 1);

const d2 = new Date(2021, 0, 2);

d1 < d2; // true

d1 <= d2; // true

d1 > d2; // false

d1 >= d2; // false

In these cases, d1 and d2 are automatically converted to timestamps for comparison.

Chapter 1.3: Subtracting Dates

Another method involves subtracting one date from another and evaluating the outcome:

const d1 = new Date(2021, 0, 1);

const d2 = new Date(2021, 0, 2);

console.log(d1 - d2 === 0); // false

console.log(d1 - d2 < 0); // true

console.log(d1 - d2 > 0); // false

This subtraction works because both d1 and d2 are treated as timestamps.

Chapter 1.4: Comparing Year, Month, and Day

For a more granular comparison, you can analyze the year, month, and day of the date objects:

const d1 = new Date(2021, 0, 1);

const d2 = new Date(2021, 0, 2);

const isSameDate = d1.getFullYear() === d2.getFullYear() &&

d1.getDate() === d2.getDate() &&

d1.getMonth() === d2.getMonth();

In this example, getFullYear, getDate, and getMonth are utilized to extract the respective components of each date.