JS: jQuery Validate Method Only One

jquery-validate-only-one.js

$.validator.addMethod('onlyOne', function(value, element, params) {

	var _this = this,
		$element = $(element),
		siblingsSelector = params[1],
		scopeSelector = params[2],
		repeated = false,
		$repeat,
		$elements = $element.closest(scopeSelector).find(siblingsSelector).not(element),
		$elementsFirst = $elements.eq(0),
		validator = $elementsFirst.data('validate_only_one') ? $elementsFirst.data('validate_only_one') : $.extend({}, this);

	$elementsFirst.data('validate_only_one', validator);

	$repeat = $elements.filter(function() {
		return value === $(this).val();
	});

	if (!$element.data('being_validated')) {

		$elements.data('being_validated', true);

		$elements.each(function() {
			validator.element(this);
		});

		$elements.data('being_validated', false);
	}

	return this.optional(element) || !$repeat.length;
}, '{0}');