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Age Calculator using JavaScript

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by Abdul Rawoof A R dot icon Updated: Feb 5, 2024

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You can use the Date item to decide the date. Then, subtract the birth date from the current date to calculate their age. JavaScript is a programming language. 


We use it to add interactivity and other dynamic features to websites. Developers use JavaScript to create web pages and applications. It works with HTML and CSS. It can respond to user input. It can regulate the behavior of page elements and interact with other web services.  

We need the user's input of a date (date of birth). The output will be the time elapsed between the user's input and the current date. We will use years, months, and days to determine the age. We will develop an HTML form to collect the user's birth date. Then, we will use JavaScript to determine the user's age. It will accept dynamic user input.  


Here is an example of how to create an age calculator using JavaScript: 

Fig 1: Preview of the output that you will get on running this code from your IDE.

Code

Birthday Calculator (with months and days) using javascript

JavaScriptdotLines of Code : 68dotLicense : Strong Copyleft (CC BY-SA 4.0)

<script>
function calculateDiff(){
  var FromYear = parseInt(document.getElementById("FromYear").value);
  var FromMonth = parseInt(document.getElementById("FromMonth").value);
  var FromDay = parseInt(document.getElementById("FromDay").value);


  //current date
  var today = new Date();
  var ToYear = today.getFullYear();
  var ToMonth = today.getMonth() + 1;
  var ToDay = today.getDay()
  var years, months, days;

  //months
  months = ToMonth - FromMonth;
  if(ToDay < FromDay) {
    months = months -1;
  }


  //years
  years = ToYear - FromYear;
  if(ToMonth < FromMonth) {
    years = years - 1;
    months = months + 12;
  }

  //days
  days = Math.floor(31 - (FromYear + years, FromMonth + months - 1, FromDay));

  //answer order
  var answer = years + " years, " + months + " months, and " + days + " days.";

  //post answer
  document.getElementById("result").textContent =  answer;
  return {years: years, months: months, days: days};
}
</script>



   <table>
        <tbody>
        <tr class="header">
          <th>&nbsp;</th>
          <th>Year</th>
          <th>Month</th>
          <th>Day</th>
        </tr>
        <tr>
       <th>Birth Date</th>
          <td><input  id="FromYear"  placeholder="YYYY" value=""></td>
          <td><input  id="FromMonth" placeholder="MM" value=""></td>
          <td><input  id="FromDay"   placeholder="DD" value=""></td>
        </tr>

        <tr>
          <th colspan="4">
            <button id="calculateDiff" onclick="calculateDiff()">Calculate</button>
          </th>
        </tr>
        <tr colspan="4">
          <th>You are <div id="result"></div></th>
      </tr>
      </tbody>
    </table>

Instructions

Follow the steps carefully to get the output easily.

  1. Create html file in your IDE.
  2. Copy the code snippet using 'copy' button and paste it in that HTML file.
  3. Run your html file directly from your file location.


Note: Use style tag to customize your table as like you want.


I found this code snippet by searching for 'age calculator using javascript', you can try any such use case!

Environment Tested

I tested this solution in the following versions. Be mindful of changes when working with other versions.

  1. The solution is created in Visual Studio Code 1.73.1.
  2. The solution is tested on node v18.12.1 and npm v8.19.2.


Using this solution, we are able to create age caculator simply using javascript with simple steps. This process also facilities an easy way to use, hassle-free method to create a hands-on working version of code which would help us to calculate the age of a particular person using javascript.

FAQ

1. How do I calculate age using JavaScript? 

You can subtract the birth year from the current year and handle edge cases like the birth month and day. 


2. What's the best way to confirm the input data in an age calculator? 

Use JavaScript's Date object to ensure the entered date is in a valid format. Check for both format and logical validity. 


3. How can I handle leap years when calculating age? 

Consider the extra day in a leap year by checking if the birthdate has already occurred in the current year. 


4. Can I calculate age with the birth year? 

For a more precise age calculation, include the birth month and day. This ensures accuracy, especially around birthdays. 


5. How do I display the calculated age on a webpage using JavaScript? 

Create an HTML element, like a <span>. Update its content with the calculated age using JavaScript. 

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