difference between function($) and $(function())

Question

What is the difference between function($) and $(function())?

Is this code redundant?

(function($) {
    "use strict"; 

  $(function() {
      run_code();
  });

})(jQuery);

Are they both document ready functions?

The first one is an IIFE that takes jQuery as a parameter to protect code inside from the global `$` variable being overwritten. The second is using jQuery. — VLAZ, Oct 24 '19 at 18:24
Is is redundant? Is function($) a document ready function like $(function())? — user2012677, Oct 24 '19 at 18:25
As for "redundant" it's hard to say. It's a defensive coding technique that *might* be unneeded but it's super cheap and at worse adds few characters without harming much. — VLAZ, Oct 24 '19 at 18:26
The outer wrapper probably serves to protect that JavaScript from potentially hostile third-party JavaScript that may seek to redefine `$` arbitrarily. — tadman, Oct 24 '19 at 18:27
[it's an IIFE](https://stackoverflow.com/questions/8228281/what-is-the-function-construct-in-javascript) not a document ready function - it will be executed ASAP. — VLAZ, Oct 24 '19 at 18:27

JLRishe · Accepted Answer · 2019-10-24T18:39:35.257

They may look similar, but they are completely unrelated.

This is called an Immediately Invoked Function Expression (IIFE). These are not specific to jQuery, but in this case, it ensures that within the body of this function, $ will refer to jQuery, even if something outside the function has overwritten the global $ variable with something else. It is a defensive practice for minimizing conflicts with other libraries.

An additional benefit is that any variables declared within this function will not be added to the global scope. Even without jQuery, this is a common practice used to help modularize code and avoid polluting the global scope.

(function($) {
    "use strict"; 


})(jQuery);

This tells jQuery to execute the specified function when the DOM is "ready":

$(function() {
    run_code();
});

difference between function($) and $(function())

1 Answers1