JavaScript: Calculate age

JavaScript Datetime: Exercise-18 with Solution

Calculate Age

Write a JavaScript program to calculate age.

Test Data:
console.log(calculate_age(new Date(1982, 11, 4)));
35
console.log(calculate_age(new Date(1962, 1, 1)));
56

Sample Solution:

JavaScript Code:

// Define a JavaScript function called calculate_age with parameter dob (date of birth)
function calculate_age(dob) { 
    // Calculate the difference in milliseconds between the current date and the provided date of birth
    var diff_ms = Date.now() - dob.getTime();
    // Create a new Date object representing the difference in milliseconds and store it in the variable age_dt (age Date object)
    var age_dt = new Date(diff_ms); 
  
    // Calculate the absolute value of the difference in years between the age Date object and the year 1970 (UNIX epoch)
    return Math.abs(age_dt.getUTCFullYear() - 1970);
}

// Output the calculated age for a person born on December 4, 1982
console.log(calculate_age(new Date(1982, 11, 4)));

// Output the calculated age for a person born on February 1, 1962
console.log(calculate_age(new Date(1962, 1, 1)));

Output:

35
56

Explanation:

In the exercise above,

• The code defines a JavaScript function named "calculate_age()" with one parameter 'dob', which represents the date of birth of a person.
• Inside the function:
• It calculates the difference in milliseconds between the current date (Date.now()) and the provided date of birth (dob.getTime()), and stores it in the variable 'diff_ms'.
• It creates a new Date object ('age_dt') representing the difference in milliseconds, essentially creating a date object that corresponds to the person's age.
• It calculates the absolute value of the difference in years between the year stored in the 'age_dt' object and the year 1970 (which is the UNIX epoch, used as a reference point).
• It returns the calculated age.
• The code then demonstrates the usage of the "calculate_age()" function by calling it with two different dates of birth:
• December 4, 1982 (new Date(1982, 11, 4))
• February 1, 1962 (new Date(1962, 1, 1))

Flowchart:

Live Demo:

See the Pen JavaScript - Calculate age-date-ex-18 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that calculates age in years by subtracting the birth date from the current date.
• Write a JavaScript function that takes a Date object representing birthdate and returns the age by comparing year, month, and day.
• Write a JavaScript function that uses the difference in milliseconds between two dates to compute age.
• Write a JavaScript function that validates the birth date to ensure it is not in the future before calculating age.

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