CODEWITHSUNDEEP
javascriptdrop-down-menu
user3325043
user3325043

Reputation:

getting the value of the selected DropDown menu option

So i know there have been many posts about this and ive read them, but the solutions recommended in this previous posts, dont work.

I have a function that dynamically creates me a drop down menu. Here it is:

function date(start, end) {

    output ="";
    for(i=start;i<=end;i++)
    {
    output += "<option value='"+i+"'>"+i+"</option>";
    }

    document.write(output);

}

And i call it like this:

Month:
        <select name="mm" id="mm" disabled onchange="activateDate();">
            <script type="text/javascript">
                date(1,12);
            </script>
        </select>

Note: activateDay just changes the attribute disabled in the next dropdown menu, because you should first select a year, then a month, then a day.

and when i try to get the selected value of the month so that i can give a month a number of days (31 for january, 28 for february)like this :

var a = document.getElementById("mm");
var month = a.options[a.selectedIndex].value;

And if i use this vars for a switch which looks for the month and returns the number of the days, then i give the number of days to my date() i get an empty drop down menu for my dates. The Javascript console in chrome says this:

Uncaught TypeError: Cannot read property 'options' of null

And points me to this line: 

var month = a.options[a.selectedIndex].value;

So what am i doing wrong?

Upvotes: 0

Views: 1522

Answers (2)

Oriol
Oriol

Reputation: 288680

The error

Cannot read property 'options' of null

means that a is null in a.options[a.selectedIndex].value.

Since you have an element with id="mm", check if:

  • Some script has hijacked window.document
  • Some script has hijacked document.getElementById
  • Some script has deleted your select, or changed its id
  • You use var a = document.getElementById("mm") before loading the select to the DOM

Probably its the last one, try running your code at onload event, or place your script just before closing </body>.

Upvotes: 1

Eldwin Eldwin
Eldwin Eldwin

Reputation: 1104

try to use this code

var month = a.options[a.selectedIndex-1].value;

Upvotes: 0

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