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getSelectedIndexes

It is possible, however, to select more than one option in a list box (but not in a combo box) by setting the

multiple

attribute of the

element to

“multiple”

</select>

If multiple options are selected,

selectedIndex

contains the index of the first selected item, but that

really doesn’t help. What you need is a way to get the indexes of all the selected options. For this, you

need a custom method, which is the first for the

ListUtil

object.

The

getSelectedIndexes()

method takes advantage of another special property of the

element: the

selected

property. The HTML DOM defines the

selected

property as a Boolean value

indicating whether the individual option is selected. So, all that is necessary is to loop through the

options of a list box and test to see if they are selected or not. If so, you need to save that index into an

array that will ultimately hold the indices of all selected options.

This method needs only one argument, the list box to check:

ListUtil.getSelectedIndexes = function (oListbox) {

var arrIndexes = new Array;

for (var i=0; i < oListbox.options.length; i++) {

if (oListbox.options[i].selected) {

arrIndexes.push(i);

}

return arrIndexes;

};

The

getSelectedIndexes()

method can then be used to either retrieve the indexes of the selected

options or, using the length of the returned array, to determine how many options are selected:

var oListbox = document.getElementById(“selListbox”);

var arrIndexes = ListUtil.getSelectedIndexes(oListbox);

alert(“There are “ + arrIndexes.length + “ option selected.”

+ “The options have the indexes “ + arrIndexes + “.”);

This code first gets a reference to the list box with the ID

“selListbox”

and then retrieves the selected

indexes and stores them in

arrIndexes

. The alert displays the a message indicating the number of

selected options as well as displaying their indexes (remember, the

toString()

method of an

Array

object returns all items in a comma-separated string).

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