Confusing analysis about javascript function objects_js object-oriented

The function object in js is a fascinating thing, but because it is too flexible, it is often confusing. I will post some code below:

Most people abbreviate it like this:

Copy code The code is as follows:

function test () {}

The entire book "JSVAScript Language Essence" Write like this:

Copy code The code is as follows:

var test = function () {}

The function can be run and assigned immediately:

Copy the code The code is as follows:

var test = function () {} () // test === undefined
var test2 = function () {return 'sugar cake'}() // test2 === 'sugar cake'

But the function abbreviation cannot be run directly. The following code will report an error:

Copy the code The code is as follows:

function test() {}() // SyntaxError: syntax error

If wrapped with the "()" operator, it is normal:

Copy the code The code is as follows:

(function test () {})();

In fact, the function name test has no meaning , remove it and it becomes an anonymous function, which can still automatically execute the code in the function body. Commonly used anonymous function writing methods:

Copy code Code As follows:

(function () {})();

Anonymous functions can also be written like this, which may be more "beautiful":

Copy code The code is as follows:

(function () {}());

See this, new to it Is Brother JS going crazy? I once saw a guy who was working on the C language in my project become petrified immediately after seeing anonymous functions...