How to display checkbox values from an array javascript

I have an array of values from a dropdown button (model) that generates dynamic checkboxes (destination). However, I wanted to display different criteria depending on the selected model and checked destination. Im sorry for this question. Im new to javascript and still learning. Thanks

Javascript:

<script>
 function populate(model, destination) {
        var mod = document.getElementById(model);
        var des = document.getElementById(destination);
        des.innerHTML = "";
        if (mod.value == "model-a") {
            var optionArray = ["Model-A.1", "Model-A.2", "Model-A.3"];
        } else if (mod.value == "model-b") {
            var optionArray = ["Model-B.1", "Model-B.2", "Model-B.3"];
        } else if (mod.value == "model-c") {
            var optionArray = ["Model-C.1", "Model-C.2", "Model-C.3"];
    }

    for (var option in optionArray) {
        if (optionArray.hasOwnProperty(option)) {
            var pair = optionArray[option];
            var checkbox = document.createElement("input");
            checkbox.type = "checkbox";
            checkbox.name = pair;
            checkbox.value = pair;
            des.appendChild(checkbox);

            var label = document.createElement('label')
            label.htmlFor = pair;
            label.appendChild(document.createTextNode(pair));

            des.appendChild(label);
            des.appendChild(document.createElement("br"));    
        }
    }
}