Javascript - innerHTML not working with HTML select menus

Question

In my HTML page I have 2 select menus with IDs \"month\" and \"day\" - \"day\" is empty when the page loads, \"month\" has 12 options with values 1-12 corresponding to Janua

Answer 1

You should not be using innerHTML to modify tags. You should be using removeChild(element); and appendChild(element);

First you set your select box in a variable for legibility and editing purposes;

var select = document.getElementById('days');

Then you clear the select box

while ( select.childNodes.length >= 1 )
{
    select.removeChild(select.firstChild);       
}

Finally you fill it again with the appropriate values

for(var i=1;i<=days;i++)
{
    newOption = document.createElement('option');
    newOption.value=i;
    newOption.text=i;
    select.appendChild(newOption);
}

So at the end with your code and my code here you get the following:

function showOutboundDays(month, year)
{
    var days=null;

    if(month==4 || month==6 || month==9 || month==11)
        days=30;
    else if(month==2)
    {
        //Do not forget leap years!!!
        if(year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) //Provided by Justin Gregoire
        {
            days=29;
        }
        else
        {
            days=28;
        }
    }
    else 
        days=31;


    var select = document.getElementById('days');

    while ( select.childNodes.length >= 1 )
    {
        select.removeChild(select.firstChild);       
    }

    for(var i=1;i<=days;i++)
    {
        newOption = document.createElement('option');
        newOption.value=i;
        newOption.text=i;
        select.appendChild(newOption);
    }
}

Leap years are now included!