Preview in the script

Hello. I have been trying to implement the preview checkbox for quite some time (when it is active, it should show the result that will be displayed). Is it possible to implement this at all? Here is a test script where I tried to do it, but I always get the error ‘Cannot handle the request because a modal dialog or alert is active’.

var dialog = new Window("dialog", "test");
dialog.orientation = "column";
dialog.alignChildren = "left";

var groupSize = dialog.add("group");
groupSize.orientation = "row";
groupSize.alignChildren = "top";

var groupWidth = groupSize.add("group");
groupWidth.orientation = "column";
groupWidth.alignChildren = "left";
groupWidth.add("statictext", undefined, "Width:");
var widthInput = groupWidth.add("edittext", undefined, "10");
widthInput.characters = 10;

var groupHeight = groupSize.add("group");
groupHeight.orientation = "column";
groupHeight.alignChildren = "left";
groupHeight.add("statictext", undefined, "Height:");
var heightInput = groupHeight.add("edittext", undefined, "10");
heightInput.characters = 10;

var previewCheck = dialog.add("checkbox", undefined, "Preview");

var groupButtons = dialog.add("group");
groupButtons.orientation = "row";
var okButton = groupButtons.add("button", undefined, "OK", {name: "ok"});
var cancelButton = groupButtons.add("button", undefined, "Відміна", {name: "cancel"});

var rectangle = null;
function createRectangle() {
    if (rectangle !== null) {
        rectangle.remove();
        rectangle = null;
    }
    try {
        var width = Number(widthInput.text) * 2.834645669;
        var height = Number(heightInput.text) * 2.834645669;
        if (app.documents.length == 0) {
            alert("Error");
            return;
        }
        
        var doc = app.activeDocument;
        var page = doc.pages[0];
        rectangle = page.rectangles.add({
            geometricBounds: [
                page.bounds[0] + (page.bounds[2] - page.bounds[0] - height) / 2,
                page.bounds[1] + (page.bounds[3] - page.bounds[1] - width) / 2,
                page.bounds[0] + (page.bounds[2] - page.bounds[0] + height) / 2,
                page.bounds[1] + (page.bounds[3] - page.bounds[1] + width) / 2
            ],
            strokeWeight: 1,
            strokeColor: doc.swatches.item("Black")
        });
        
    } catch(e) {
        alert("Error: " + e);
    }
}

previewCheck.onClick = function() {
    if (this.value && widthInput.text && heightInput.text) {
        createRectangle();
    } else if (!this.value && rectangle !== null) {
        rectangle.remove();
        rectangle = null;
    }
}

widthInput.onChanging = heightInput.onChanging = function() {
    if (previewCheck.value) {
        createRectangle();
    }
}

if (dialog.show() == 1) { // OK
    if (rectangle === null) {
        createRectangle();
    }
} else { // Cancel
    if (rectangle !== null) {
        rectangle.remove();
    }
}

 What do I need to fix?