How to calculate a person's age based on their birthdate using JavaScript?

You can calculate a person's age based on their birthdate using JavaScript by following these steps:

Get the current date
Get the birthdate of the person
Subtract the birthdate from the current date to get the difference in milliseconds
Convert the difference in milliseconds to years
Return the calculated age

Here is an example code snippet to calculate the age in JavaScript:

function calculateAge(birthdate) {
  // Step 1: Get the current date
  var currentDate = new Date();

  // Step 2: Get the birthdate of the person
  var birthdate = new Date(birthdate);

  // Step 3: Subtract the birthdate from the current date to get the difference in milliseconds
  var differenceInMilliseconds = currentDate - birthdate;

  // Step 4: Convert the difference in milliseconds to years
  var ageDate = new Date(differenceInMilliseconds);
  var calculatedAge = Math.abs(ageDate.getUTCFullYear() - 1970);

  // Step 5: Return the calculated age
  return calculatedAge;
}

// Example usage
var birthdate = "1990-12-31"; // Format: "yyyy-mm-dd"
var age = calculateAge(birthdate);
console.log(age); // Output: The person's age based on the birthdate

In this example, the calculateAge function takes the birthdate as an argument in the format "yyyy-mm-dd". It then returns the calculated age based on the birthdate. The age is calculated by finding the difference between the current date and the birthdate, converting it into years, and returning the result.