how should i remove value in list box when i checked

[kesava chaitanya]

hi
when i Checked dropbox the Value "Cash" in listbox should be removed;for that i have written code like this;i am able to remove "Cash" from list box but i am getting space in the list box;how should i remove space in the list box;
any help?

html
Script language="JavaScript"
function checkEntryType(){

if(document.frm.dropbox.checked == true)
{
for(var i=0;i document.frm.mode.length;i++){
if(document.frm.mode.options[i].text == "Cash"){
document.frm.mode.options[i].text=""
document.frm.mode.options[i].value=""

}
}
}



}
/script
form name=frm method=get action=""
Drop Box input type=checkbox name=dropbox value=drop
Mode of Payment
select name="mode"
option value=""/option
option value="Cash"Cash/option
option value="Cheque"Cheque/option
option value="Demand_Draft"Demand Draft/option
/form
/html

[kesava chaitanya]

hi
sorry i forgot to add one line in the above code
Drop Box<input type=checkbox name=dropbox value=drop on
click=checkEntryType()

[John Hembree]

Here's something from the Quick References section on DevGuru.com:
You can use the options array to add options to, or delete options from any Select object. When adding or altering an option, you assign an Option object to a particular element of the array. The following code first creates an Option object called Folk, and then assigns it to element # 3 of the options array of a user-defined Select object called MusicType. If there is a value already assigned to element 3, it will be replaced by Folk, otherwise it will be created along with undefined elements at every index between the one created and the last existant one.

Code:
document.forms[0].musicType.options[3] = new Option("Folk", "folk", false, false)

Similarly, you can delete any option by assigning the value null to the appropriate element of the options array:

Code:
document.forms[0].musicType.options[2] = null

This will have the effect of removing element # 2 from the options array, and at the same time compressing the array so that element # 3 becomes # 2, element # 4 becomes # 3 etc. After deleting an option you must refresh the document by using history.go(0) at the end of the code. To determine which option of a Select object is currently selected, you can use the selectedIndex property along with the options property as follows:

Code:
document.forms[0].musicType.options.selectedIndex

...or you could simply use the selectedIndex property of the Select object:

Code:
document.forms[0].musicType.selectedIndex

Both the above lines of code return the number of the currently-selected index. If, however, the Select object allows for multiple selections (i.e. when the <SELECT> tag includes the MULTIPLE attribute), the selectedIndex property will only return the index of the first option selected. To determine all of the selected options, you would have to loop through the options array testing each option individually.