jQuery validate plugin, check input defaultValue

Question

Trying to validate a field using jquery validate plugin. All I want to check if the current input value is not equal to defaultValue. If it is equal then its not valid, clean the value and show the error message.

Something like that:

...

firstname:{
    required: function(element){                       
    return element.val() !== element.defaultValue;
    element.val('');
    }                                          
}

...

Unfortunately that does not work.

Answer 1

Ok, found a solution. Simply creating a following method solves the issue.

jQuery.validator.addMethod("defaultInvalid", function(value, element){
    return !(element.value == element.defaultValue);
},jQuery.validator.messages.required);

Answer 2

Here's an implementation that works for radio buttons as well:

var isChanged = function ($element) {
    switch ($element.attr('type')) {
        case "radio":
            var $formElementsWithSameName = $element.closest('form').find(':input').filter(function () {
                return $(this).attr('name') == $element.attr('name');
            });
            return $formElementsWithSameName.filter(':checked').filter(function () {
                return $(this).prop('defaultChecked');
            }).length == 0;

        case "text":
            return $element.val() != $element.prop('defaultValue');
        default:
            console.error("No implementation of isChanged for element " + $element);
    }
};