Question

I am very new to Javascript so please be patient. I have a script that is to check if certain form elements are null. If any of the form elements are null, an alert should be shown. However, nothing happens. I have looked at a copious amount of examples, cannot seem to get past this problem.

The script in question is shown below:

var age;
var todaysDate;
var birthDate;
var inputOk;

function setDates() {
    if (d.value !== null && m.value !== null && y.value !== null) {
    inputOk = true;

    var day = d.value;
    var month = m.value + 1;
    var year = y.value;
    var today = new Date();
    var dob = new Date(year, month, day);

    todaysDate = today.valueOf();
    birthDate = dob.valueOf();
}
else {
    inputOk = false;
}   
}

function calculateAge() {

}

function outputAge() {
    //var output = document.getElementById('ageOut');
    //document.write('You are aged: '+age);
}

function getAge() { 
setDates();

if (inputOk) {
    calculateAge();
    outputAge();    
}
else {
    alert("Please enter your D.O.B correctly.");
}  
}

The HTML form in question is shown below:

<form name ="dob" id="dobform">
   <select id="d">
 <option value="null">Day</option>
   </select>
   <select id="m">
 <option value="null">Month</option>
   </select>
   <select id="y">
 <option value="null">Year</option>
   </select>
   <input type="button" value="Get my age!" onclick="getAge();"/>
</form>

Answer 1

Accessing your dom elements directly by id is a bad idea. I believe it will work on some versions of IE, but the standard way is to call document.getElementById("idOfYourControl")

So to get the value of your “m” select:

var mSelect = document.getElementById("m");
mSelect.value;

So your function would look like:

function setDates() {
    var dSelect = document.getElementById("d");
    var mSelect = document.getElementById("m");
    var ySelect = document.getElementById("y");

    if (dSelect.value !== "null" && mSelect.value !== "null" && ySelect.value !== "null") {
        inputOk = true;

        //and so on
}