How to Compare Dates Accurately in JavaScript?

Comparing Dates in JavaScript

In JavaScript, comparing dates can be a straightforward task using the built-in Date object. Here's a comprehensive guide on how to compare the values of two dates:

Greater Than, Less Than, and Not in the Past

To compare the values of two dates, you can create a Date object for each date, then use the >, <, <= or >= operators. For instance:

const date1 = new Date('2023-03-08');
const date2 = new Date('2023-04-05');

console.log(date1 > date2); // false
console.log(date1 < date2); // true

Equality and Inequality

To check for equality or inequality, you can use the ==, !=, ===, and !== operators. However, using these operators directly with Date objects won't work correctly. Instead, you should use date.getTime() to compare the numerical representation of the dates:

const d1 = new Date();
const d2 = new Date(d1);

console.log(d1 == d2); // false (wrong!) 
console.log(d1 === d2); // false (wrong!)
console.log(d1 != d2); // true (wrong!)
console.log(d1 !== d2); // true (wrong!)
console.log(d1.getTime() === d2.getTime()); // true (correct)

Input Validation

To avoid input validation issues, it's advisable to use drop-downs or other constrained forms of date entry instead of text boxes. This ensures that the user provides dates in a consistent format that can be easily parsed and compared.

date.getTime() Documentation

For further reference, here's the documentation for date.getTime():

Returns the numeric value of the specified date as the number of milliseconds since January 1, 1970, 00:00:00 UTC. (Negative values are returned for prior times.)

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