Placeholder polyfill (jQuery)

placeholder-polyfill.js

function placeholderPolyfill(el, opt){
    opt = opt || {};
    var $el = $(el),
        testAttribute = function(element, attribute) {
            var test = document.createElement(element);
            return (attribute in test);
        };
    if (!testAttribute('input','placeholder') && $el.attr('placeholder').length) {
        var defaults = {
            clearOnSubmit: true
        };
        opt = $.extend({}, defaults, opt);
        var placeholder = $el.attr('placeholder');
        if (!$el.val().length)
            $el.val(placeholder);
        $el.focus(function(){
            if ($(this).val() == placeholder)
                $(this).val('');
        }).blur(function(){
            if (!$(this).val().length)
                $(this).val(placeholder);
        });
        if (opt.clearOnSubmit) {
            $el.closest('form').bind('submit.placeholder', function(){
                if ($el.val() == placeholder)
                    $el.val('');
            });
        }
    }
}