I'm working on a UserScript that adds Buttons to a webpage. One of the buttons I'm working on when clicked will create a popup div. I'm trying to create a dynamic Select/Option dropdown list within the popup, with the options coming from an Array. For the second drop down list I'm trying to create a dynamic drop down list based on the selection in the previous dropdown list, but I'm unsure how to proceed. I'd like the itemDropList's options to be dynamically created based upon the value of the selected option in the typeDropList.

Thanks in advance!

This is my code so far:

var button = document.createElement('button'),
button.onclick = prompt;
function prompt() {
    var blockingDiv = document.createElement('div');
    blockingDiv.id = 'PopupBackground';
    var divPopup = document.createElement('div');
    divPopup.id = 'better1ClickSimTChangeCTIPopup';
    var content = document.createElement('div');
    content.id = 'Content';
    var typeDropList = document.createElement('select');
    typeDropList.id = 'TypeDropList';
    typeDropList.name = 'TypeDropList';
    typeDropList.onchange = changeItem(this.value);
    content.appendChild(typeDropList);
    var typeOptions =
        [
            {
                "text": 'Select Type',
                "value": '',
                "defaultSelected": true,
                "selected": true
            },
            {
                "text": 'Text 1',
                "value": 'A',
                "defaultSelected": false,
                "selected": false
            },
            {
                "text": 'Text 2',
                "value": 'B',
                "defaultSelected": false,
                "selected": false
            },
            {
                "text": 'Text 3',
                "value": 'C',
                "defaultSelected": false,
                "selected": false
            }
        ];
    for (var i = 0; i < typeOptions.length; i++) {
        var typeOption = document.createElement('option');
        typeOption.id = 'TypeOptions';
        typeOption.name = 'TypeOptions';
        var type = typeOptions[i];
        typeOption.appendChild(new Option(type.text, type.value, type.defaultSelected, type.selected));
        typeDropList.appendChild(typeOption);
    }
    var itemDropList = document.createElement('select');
    itemDropList.id = 'ItemDropList';
    content.appendChild(itemDropList);
    var typeItemOptions =
    {
        A: ['Item A 1',
            'Item A 2',
            'Item A 3'],
        B: ['Item B 1',
            'Item B 2',
            'Item B 3'],
        C: ['Item C 1',
            'Item C 2',
            'Item C 3']
    };