自动执行匿名 JavaScript 函数的括号位置? [英] Location of parenthesis for auto-executing anonymous JavaScript functions?

问题描述

我最近比较了 json2.js 与我在项目中使用的版本相比，我注意到函数表达式的创建和自执行方式有所不同.

I was recently comparing the current version of json2.js with the version I had in my project and noticed a difference in how the function expression was created and self executed.

用于将匿名函数包裹在括号中然后执行的代码，

The code used to wrap an anonymous function in parenthesis and then execute it,

(function () {
  // code here
})();

但现在它将自动执行的函数包装在括号中.

but now it wraps the auto-executed function in parenthesis.

(function () {
  // code here
}());

在解释JavaScript的封装匿名函数语法的接受答案中，CMS有一条评论 表明(function(){})(); 和 (function(){}()); 都是有效的."

There is a comment by CMS in the accepted answer of Explain JavaScript’s encapsulated anonymous function syntax that "both: (function(){})(); and (function(){}()); are valid."

我想知道有什么区别?前者是否通过留下全局匿名函数来占用内存?括号应该放在哪里?

I was wondering what the difference is? Does the former take up memory by leaving around a global, anonymous function? Where should the parenthesis be located?

推荐答案

它们几乎相同.

第一个函数用括号括起来，使其成为一个有效的表达式并调用它.表达式的结果未定义.

The first wraps parentheses around a function to make it a valid expression and invokes it. The result of the expression is undefined.

第二个执行函数，自动调用周围的括号使其成为有效的表达式.它也评估为未定义.

The second executes the function and the parentheses around the automatic invocation make it a valid expression. It also evaluates to undefined.

我不认为有一种正确"的方法可以做到，因为表达式的结果是相同的.

I don't think there's a "right" way of doing it, since the result of the expression is the same.

> function(){}()
SyntaxError: Unexpected token (
> (function(){})()
undefined
> (function(){return 'foo'})()
"foo"
> (function(){ return 'foo'}())
"foo"

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