Compulsory option of jQuery plugin
<p>I am making my custom jQuery plugin whose code is this:</p>

<pre><code>(function($) {

    $.fn.foo = function(options) {
        var opt = $.extend({}, $.fn.foo.defaults, options);

        return this.each(function() {
            //do operation with opt
        });

    });


    $.foo.defaults = {
        item1:'value1',
            item2:'value2',
            item3:'value3',
        };

})(jQuery);
</code></pre>

<p>It will be implemented like this:</p>

<pre><code> //Implementation
 $(...).foo({
      item1:'value1',
      item2:'value2',
      item3:'value3',
      item4:'value4',
 });
</code></pre>

<p>My question is that how can I make <em>item4</em> value to be compulsory? I want that user must enter value for <em>Item4</em> . In my plugin I need to do some operations with item4 so how can it be made compulsory. I will be having one or more items too which should be compulsory. Is there any way by which I can warn user if the that value is not passed by the user ? </p>
