error with getTime() in javascript

Question

I'm new to javascript. I'm trying to create a page that has an input option for date of birth. Once the submit button is clicked, I want to verify that the person is not underage (above 18).

This is my HTML code

<form id="myForm" method="get" action="#">

  <p>Date of birth: <input type="date" name="dob" value="MM-DD-YYYY" required></p>

  <p><input type="submit" value="submit" onclick="return validate_date_of_birth()">
</form>

and this is my javascript function:

function validate_date_of_birth(){
    var dob = document.forms["myForm"]["dob"].value;
    var ageDifMs = Date.now() - dob.getTime();
    return true;
}

I'm getting a problem with dob.getTime(). Note that I'm not really verifying the age in the above code. That would require an if loop to verify the age. I'm stuck at a point where the difference is not being calculated. I tried to check the values of Date.now() and dob.getTime() by using the alert() function in javascript. For dob.getTime(), the value it prints out is "undefined". What am I doing wrong?

try this https://stackoverflow.com/questions/10008050/get-age-from-birthdate — user5091906, Sep 04 '17 at 03:24

score 1 · Accepted Answer · answered Sep 04 '17 at 03:13

.getTime() is a method of Date/Time object in JavaScript.

var dob = document.forms["myForm"]["dob"].value; is not a valid Date object as this is a string.

which caused you an error in dob.getTime().

to prevent the error simply parse dob to Date first after setting it.

var dob = new Date(document.forms["myForm"]["dob"].value);

OR

var dob = document.forms["myForm"]["dob"].value;
dob = new Date(dob);

hope that helps

score 0 · Answer 2 · answered Sep 04 '17 at 03:16

You used getTime() on the input value, but you need to use it on a Date object. For this, construct a Date object from the input value, and then you'll be able to get the time on it. Be careful though, Date needs to be in one of these formats :

YYYY-MM-DD
MM/DD/YYYY
Mar 25 2015
Wednesday March 25 2015

otherwise you'll get an error. You can obviously receive any format and then reformat it to what you need though.

function validate_date_of_birth(){
    var dob = document.forms["myForm"]["dob"].value;
    var ageDifMs = Date.now() - new Date(dob).getTime(); // we make a new Date object from dob
    console.log(ageDifMs);
    return false; // so we can see the result and not be redirected
}

<form id="myForm" method="get" action="">

  <p>Date of birth: <input type="date" name="dob" value="YYYY-MM-DD" required></p>

  <p><input type="submit" value="submit" onclick="return validate_date_of_birth()">
</form>

Date reference

error with getTime() in javascript

2 Answers2