Prevent Default is not happening in Phone Call Activity form on Save

Hi All,

I am using MS Dynamics CRM 2016 online.

My requirement is, based on regarding field value in Phone call entity form (when activity created) i need to restrict users with an alert message and prevent the form from saving.

Issue:

Phone Call activity is getting saved even after i write the PrventDefault() line.

here is my code:

I am passing execution Context parameter from JavaScript

var req = new XMLHttpRequest();
req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v8.2/incidents(" + regardingObjectId + ")?$select=status", true);
req.setRequestHeader("OData-MaxVersion", "4.0");
req.setRequestHeader("OData-Version", "4.0");
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.setRequestHeader("Prefer", "odata.include-annotations=\"*\"");
req.onreadystatechange = function () {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var result = JSON.parse(this.response);
var status = result["status"];
var status_formatted = result["status@OData.Community.Display.V1.FormattedValue"];
if (status == "open")
{
alert('The Status is still open');
executeObject.getEventArgs().preventDefault();
if (executeObject.getEventArgs().isDefaultPrevented())
{
return;
}

}
} else {
Xrm.Utility.alertDialog(this.statusText);
}