How to get SPFieldChoice values using rest api SharePoint 2013

Referrence link: sharepoint.stackexchange.com

var context = new SP.ClientContext.get_current();
var web = context.get_web();
context.load();

// Get task list
var taskList = web.get_lists().getByTitle("Tasks");

// Get Priority field (choice field)
var priorityField = context.castTo(taskList.get_fields().getByInternalNameOrTitle("Priority"),
                                   SP.FieldChoice);

// Load the field
context.load(priorityField);

// Call server
context.executeQueryAsync(Function.createDelegate(this, this.onSuccessMethod),
                          Function.createDelegate(this, this.onFailureMethod));  

function onSuccessMethod(sender, args) {
    // Get string arry of possible choices (but NOT fill-in choices)
    var choices = priorityField.get_choices();
    alert("Choices: (" + choices.length + ") - " + choices.join(", "));
}

function onFailureMethod(sender, args) {
    alert("oh oh!");
}