Bootstrap the function in the source code plus the + number

In general, the jquery plugin is written in this way

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

Today, I saw Bootstrap's JavaScript component written like this.

!  function($) {  window.jquery);  

Why add a "!" in front of you?

As we all know, there are two ways to declare a function

function fnA(){alert(‘msg‘);}//声明式定义函数var fnB = function(){alert(‘msg‘);}//函数赋值表达式定义函数

The two functions that appear in the landlord problem are anonymous functions. Usually, the way we call a method is functionname ()

However, if we try to add () to the end of a defined function, the parser is incomprehensible.

function msg(){  alert(‘message‘);}();//解析器是无法理解的

The calling method of the defined function should be MSG (); So why wrap the function body part in ()?

It turns out that using parentheses to define the function body, the parser will invoke the definition function in the form of a function expression. In other words, any function that can be turned into a function expression can make the parser call the definition function correctly. and! is one, and the +-| | have such a function.

In addition, use! Perhaps more of a habit problem, different operators, performance is different.

Just to be able to omit a character ...

This will result in an error, because this is a function definition: Functions() {} ()//Common (more than one pair of parentheses), call anonymous function: (function() {})// But in front of a Boolean operator (only one more exclamation point), is the expression, will execute the following code, also legitimate implementation of the call! function() {} ()       

Bootstrap the function in the source code plus the + number