传递jQuery作为参数

Question

If JQuery does exist in scope will these behave in the same way?

The $ is used to constrain the scope to inside each function I guess, I'm not exactly sure why however. The second snippet is the original code, I'm attempting to add a check for jquery before it's called as in the first snippet.

First:

(function () {
            if (!window.jQuery) {
                alert('Error: JQuery not loaded.');
             return;
            }
            main(jQuery);
        })();
        function main($, undefined) {
            alert("main 1");

            //do some work on $ 

        }

Second:

    (function ($) {
        if (!$) {
            alert('Error: JQuery not loaded.');
            return;
        }
        alert("main 2");

        //do some work on $ 

    })(jQuery);

Third (Maybe this is slightly better?):

(function () {
            if (!window.jQuery) {
                alert('Error: JQuery not loaded.');
                return;
            }
            var main = function ($, undefined) {
                alert("main 3");

                //do some work on $ 

            }
            main(jQuery);
        })();

Answer 1

This is the best solution for me.

(function () {
                if (!window.jQuery) {
                    alert('Error: JQuery not loaded.');
                    return;
                }
                var main = function ($, undefined) {
                    alert("main 3");

                    //do some work on $ 

                }
                main(jQuery);
            })();