Add operator before analyzing function to execute function immediately

We know that the function is usually called by FunctionName()

But if we try to add () to the end of a "define 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().

If you want the function to be executed immediately, you can wrap the function body with ().

This is because if you use parentheses to wrap the defined function body, the parser will call the defined function in the form of function expression. In other words, any method that can turn a function into a function expression can enable the parser to correctly call the defined function. As follows:

// 这么写会报错，因为这是一个函数定义：
function() {}()

// 常见的（多了一对括号），调用匿名函数：
(function() {})()

// 但在前面加上一个布尔运算符（只多了一个感叹号），就是表达式了，将执行后面的代码，也就合法实现调用
!function() {}()

! is just one of the operators, and + - || ~ all have such functions.

Using ! may be more of a matter of habit. Different operators have different performances.

The effect is equivalent to the following two commonly used immediate execution methods:

(function() {})();
  // or  
(function() {}());

Thank you for reading.

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