How to Check if a Date Refers to a Past Day in JavaScript

When working with dates in JavaScript, you may come across a scenario where you need to determine if a given date refers to a day in the past. Simply comparing dates using the getTime() method isn’t sufficient, as dates may have different times associated with them. This article will guide you through a solution to this problem.

To check if a date references a past day in JavaScript, you can use the following function:

const isFirstDatePastSecondDate = (firstDate, secondDate) => {
  if (firstDate.setHours(0, 0, 0, 0) - secondDate.setHours(0, 0, 0, 0) >= 0) {
    return false; // First date is in the future or today
  }
  
  return true; // First date is in the past
}

In this function, the setHours() method is used to set the time for both dates to 00:00:00. By doing so, the comparison will only consider the dates without taking the time into account.

Here’s a more concise version of the function using implicit return:

const isFirstDatePastSecondDate = (firstDate, secondDate) => firstDate.setHours(0, 0, 0, 0) - secondDate.setHours(0, 0, 0, 0) < 0;

To use this function, let’s consider an example where we compare yesterday’s date to today’s date:

const today = new Date();
const yesterday = new Date(today);
yesterday.setDate(yesterday.getDate() - 1);

console.log(isFirstDatePastSecondDate(yesterday, today)); // Output: true
console.log(isFirstDatePastSecondDate(today, yesterday)); // Output: false

In the example above, we create two date objects - today and yesterday. We set the yesterday date to the previous day by using the setDate() method with a value of yesterday.getDate() - 1. Finally, we call the isFirstDatePastSecondDate function to check if yesterday is in the past compared to today, and vice versa.

By following this approach, you can accurately determine if a given date refers to a day in the past in JavaScript.