What does the jQuery() function in jQuery do?

Question

In this video there is a snippet of code that goes something like this:

if (jQuery) {jQuery(function() {
    // ...
})}

I\'ve never seen the

Answer 1

jQuery(function()

is same as

$(document).ready(function()

if(jQuery)

is a check whether the jQuery.js file has been loaded or not.

There is another way to check this

if (typeof jQuery == 'undefined')
{
    //jQuery has not been loaded  
}