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TypeScript - compare two dates

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Created by:

Paluskitten

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In this article, we're going to have a look at how to compare two dates in TypeScript.

Quick solution:

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const date1 = new Date(2022, 10, 15);
const date2 = new Date(2022, 10, 15);
​
console.log(date1.getTime() === date2.getTime()); // true

Talking about date values comparison we need to look at the fact there are comparison operators that will be working and will not directly with date objects:

Working operators are: >, <, >= and <=,
Not working operators are: ==, ===, != and !===.

For not working operators it is necessary to use getTime() method and compare results, e.g. date1.getTime() === date2.getTime().

Common mistakes analysis:

Note: read this or this article to understans how == and === work for objects comparision.

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const now = new Date();
const date1 = new Date(now);
const date2 = new Date(now);
​
console.log( now   ==  now   ); // true  // incorrect usage !!!
console.log( now   === now   ); // true  // incorrect usage !!!
console.log( date1 ==  date2 ); // false // incorrect usage !!!
console.log( date1 === date2 ); // false // incorrect usage !!!
console.log( date1 !=  date2 ); // true  // incorrect usage !!!
console.log( date1 !== date2 ); // true  // incorrect usage !!!
​
console.log(date1.getTime() === date2.getTime()); // true // correct usage

Look at the below examples to see how to use comparison operators:

1. Bigger-smaller operators example

Edit

In this section presented example uses fact, that it is possible to check that dates are not in relation bigger or smaller, so they are equal.

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const compareDates = (a: Date, b: Date): number => {
  if (a < b) return -1;
  if (a > b) return +1;
​
  return 0; // dates are equal
};
​
​
// Usage example:
​
const now = new Date();
const date1 = new Date(2022, 1, 15);
const date2 = new Date(2022, 6, 20);
​
console.log(compareDates(now, now));     //  0 // it means dates are equal
console.log(compareDates(date1, date2)); // -1 // arg 1 is smaller (date1 < date2)
console.log(compareDates(date2, date1)); // +1 // arg 1 is bigger  (date2 > date1)

Output:

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0
-1
1

2. Equal-different operators example

Edit

The example presented in this section uses fact, if the Unix time of both dates is equal it means dates are equal.

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const compareDates = (a: Date, b: Date): boolean => {
  if (a && b) {
    return a.getTime() === b.getTime();
  }
  return false;
};
​
​
// Usage example:
​
const now = new Date();
const date1 = new Date(2022, 1, 15);
const date2 = new Date(2022, 6, 20);
​
console.log(compareDates(now, now));     // true
console.log(compareDates(date1, date2)); // false
console.log(compareDates(date2, date1)); // false