Differences in jquery $ (function () {}) and (function ($) {}) (jquery), $ (document). Ready (function () {}) detailed explanation

1. (function ($) {...}) (JQuery);

1), principle:

This is actually an anonymous function, as follows:

Function (ARG) {...}
This defines an anonymous function with the argument arg

When calling a function, the parentheses and arguments are written behind the function, and because of the precedence of the operator, the function itself needs parentheses, namely:
(function (ARG) {...}) (param)
This is equivalent to defining an anonymous function with arg parameter, and calling this anonymous function as a parameter param

(function ($) {...}) (jquery) is the same, the reason that the only use of $ in formal parameters is to not conflict with other libraries, so the argument uses jQuery
Equivalent to funtion output (s) {...};output (jQuery); or Var fn=function (s) {...}; FN (jQuery);

2), function (very useful):

The greatest advantage of this writing is the formation of closures. In (function ($) {...}) (jQuery) functions and variables defined internally can only be valid in this scope.

the concept of whether a function function or a private variable is formed. For example:

var i=3;
function init () {
    alert ("Outer init:" +i);
}
(function ($) {
	var i=2;
	function init () {
	    alert ("Inner layer init:" +i);
	}

	Init ();
}) (jQuery);
Init ();

Execution results:

Inner layer Init:2

outer Init:3

2, $ (function () {...});  JQuery (function ($) {...}); $ (document). Ready (function () {...})

These three functions are the same, I need to use the first one, simple writing.

The function to execute after the document is loaded.