blocks|key|1183479|text|它们实际上是一样的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183480|第一个函数使用圆括号将函数括起来，使其成为有效的表达式并调用它。表达式的结果是未定义的。|1183481|第二个函数执行函数，自动调用前后的圆括号使其成为有效的表达式。它的计算结果也是未定义的。|1183482|我不认为有一种“正确”的方法，因为表达式的结果是相同的。|1183483|>+function(){}()
SyntaxError:+Unexpected+token+(
>+(function(){})()
undefined
>+(function(){return+'foo'})()
"foo"
>+(function(){+return+'foo'}())
"foo"|code-block|syntax|javascript|1183484|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|R|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

They're virtually the same. 

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

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

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

<pre><code>&gt; function(){}()
SyntaxError: Unexpected token (
&gt; (function(){})()
undefined
&gt; (function(){return 'foo'})()
"foo"
&gt; (function(){ return 'foo'}())
"foo"
</code></pre>

blocks|key|1183522|text|在这种情况下，这无关紧要。您将在第一个定义中调用一个解析为函数的表达式，并在第二个示例中定义并立即调用一个函数。它们之所以相似，是因为第一个示例中的函数表达式就是函数定义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183523|对于调用解析为函数的表达式，还有其他更明显的有用情况：|1183524|(foo+%7C%7C+bar)()|code-block|syntax|javascript|1183525|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In that case it doesn't matter. You are invoking an expression that resolves to a function in the first definition, and defining and immediately invoking a function in the second example. They're similar because the function expression in the first example is just the function definition.

There are other more obviously useful cases for invoking expressions that resolve to functions: 

<pre><code>(foo || bar)()
</code></pre>

blocks|key|1183605|text|除了语法之外，没有任何区别。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1183606|关于您对第二种方法的担忧：|1183607|考虑一下：|1183608|(function+namedfunc+()+{+...+}())|offset|length|style|CODE|1183609|即使您提供了名称，namedfunc仍然不在全局作用域中。匿名函数也是如此。将其放入该作用域的唯一方法是将其赋给括号内的一个变量。|1183610|((namedfunc+=+function+namedfunc+()+{+...+})())|code-block|syntax|javascript|1183611|外括号是不必要的：|1183612|(namedfunc+=+function+namedfunc+()+{+...+})()|1183613|但无论如何你都不想要那个全球声明，对吧？|1183614|所以它可以归结为：|1183615|(function+namedfunc+()+{+...+})()|1183616|您还可以进一步减少它:名称是不必要的，因为它永远不会被使用(除非您的函数是递归的..即使这样，你也可以使用arguments.callee)|1183617|(function+()+{+...+})()|1183618|这就是我对它的看法(可能不正确，我还没有读过ECMAScript规范)。希望能有所帮助。|1183619|entityMap^0|0|0|0|0|X|0|9|9|0|0|0|0|0|0|0|1H|G|0|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1C|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1D|8|@$H|1E|I|1F|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|1G|8|@$H|1H|I|1I|J|K]]|9|@]|A|$]]|$1|N|3|O|5|P|7|1J|8|@]|9|@]|A|$Q|R]]|$1|S|3|T|5|6|7|1K|8|@]|9|@]|A|$]]|$1|U|3|V|5|P|7|1L|8|@]|9|@]|A|$Q|R]]|$1|W|3|X|5|6|7|1M|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1N|8|@]|9|@]|A|$]]|$1|10|3|11|5|P|7|1O|8|@]|9|@]|A|$Q|R]]|$1|12|3|13|5|6|7|1P|8|@$H|1Q|I|1R|J|K]]|9|@]|A|$]]|$1|14|3|15|5|P|7|1S|8|@]|9|@]|A|$Q|R]]|$1|16|3|17|5|6|7|1T|8|@]|9|@]|A|$]]|$1|18|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]]|19|$]]

There isn't any difference beyond the syntax.

Regarding your concerns about the second method of doing it:

Consider:

<code>(function namedfunc () { ... }())</code>

<code>namedfunc</code> will still not be in the global scope even though you provided the name. The same goes for anonymous functions. The only way to get it in that scope would be to assign it to a variable inside the parens.

<pre><code>((namedfunc = function namedfunc () { ... })())
</code></pre>

The outer parens are unnecessary:

<pre><code>(namedfunc = function namedfunc () { ... })()
</code></pre>

But you didn't want that global declaration anyways, did you?

So it it boils down to:

<pre><code>(function namedfunc () { ... })()
</code></pre>

And you can reduce it even further: the name is unnecessary since it will never be used (unless your function is recursive.. and even then you could use <code>arguments.callee</code>)

<pre><code>(function () { ... })()
</code></pre>

That's the way I think about it (may be incorrect, I haven't read the ECMAScript specification yet). Hope it helps.

I was recently comparing the current version of <a href="https://github.com/douglascrockford/JSON-js/blob/master/json2.js" rel="noreferrer">json2.js</a> with the version I had in my project and noticed a difference in how the function expression was created and self executed.

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

<pre><code>(function () {
 // code here
})();
</code></pre>

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

<pre><code>(function () {
 // code here
}());
</code></pre>

There is a comment by CMS in the accepted answer of <a href="https://stackoverflow.com/questions/1634268/explain-javascripts-encapsulated-anonymous-function-syntax">Explain JavaScript’s encapsulated anonymous function syntax</a> that “both: <code>(function(){})();</code> and <code>(function(){}());</code> are valid.”

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?

Location of parenthesis for auto-executing anonymous JavaScript functions?

最近，我将的当前版本与项目中的版本进行了比较，注意到函数表达式的创建和自执行方式有所不同。用于将匿名函数包装在括号中然后执行它的代码，(function () {  // code here})();但现在它将自动执行的函数包含在括号中。(function () {  // code here}());在的公认答案中有...

问自动执行匿名JavaScript函数的括号位置？
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