在JavaScript中使用匿名函数有什么缺点吗？例如。记忆用吗？ [英] Are there any drawbacks to using anonymous functions in JavaScript? E.g. memory use?
问题描述
在过去的某个时刻，我读了某些，这让我觉得JavaScript中的匿名函数会占用大量的内存（因为它们带有整个当前范围） ，而命名（静态？）函数没有这个问题。
At some point in the past, I read something that gave me the idea that anonymous functions in JavaScript can use up a surprising amount of memory (because they carry the entire current scope around with them), whereas named (static?) functions don’t have this issue.
我不记得我在哪里读到这个，所以我不能回去重新阅读并自己解决这个问题。
I can’t remember where I read this, so I can’t go back and re-read it and figure this out for myself.
我有两个问题：
- 是否存在匿名函数可以使用足够内存以使其值得关注的情况？ （如果有，你有一个例子吗？）
- 匿名函数是否有任何其他缺点（与命名/静态函数相反）？
推荐答案
所有JavaScript函数的行为方式都相同，因为它们继承了整个范围链中的变量环境，导致并包括他们自己。对于匿名和命名函数也是如此。
All JavaScript functions will behave in the same manner in that they inherit the variable environments in entire scope chain leading up to, and including, themselves. This is equally true for both anonymous and named functions.
这个对外部环境的引用链保留在每个函数中，即使函数被传递到完全不同的范围内。
This chain of references to the outer environments stays with each function, even if the function is passed into an entirely different scope.
传统上，这意味着只要内部闭包继续存在，任何给定链中的所有变量都会保留一个引用。虽然在编译代码的现代浏览器中，很可能会分析实际引用哪些变量，并且只保留那些变量，允许不再引用的其他变量被垃圾收集。
Traditionally, this would mean that all variables in any given chain have a reference retained to them as long as the inner closure continues to exist. Although in modern browsers that compile the code, it is likely that there will be an analysis of which variables are actually referenced, and only those will be retained, allowing others that are no longer referenced to be garbage collected.
但是，还有其他情况下匿名函数是浪费的。
However, there are other situations where an anonymous function is wasteful.
这是一个常见的代码：
for( var i = 0; i < 100; i++ ) {
(function( j ) {
setTimeout( function() { console.log( j ); }, 1000 );
})( i );
}
这是一种匿名函数比命名更浪费的情况函数，因为你在循环期间重新创建一个相同的函数100次，你可以重用一个命名函数。
This is a situation where an anonymous function is a bit more wasteful than a named function because you're recreating an identical function 100 times during the loop when you could just reuse a named one.
function setConsole( j ) {
setTimeout( function() { console.log( j ); }, 1000 );
}
for( var i = 0; i < 100; i++ ) {
setConsole( i );
}
这具有完全相同的闭包开销，但效率更高，因为你已经只构造了一个函数来创建每个新的变量环境。
This has the exact same closure overhead, but is more efficient because you've only constructed one function to create each new variable environment.
http://jsperf.com/immediate-vs-named （感谢 @Felix Kling 对于jsPerf。）
http://jsperf.com/immediate-vs-named (Thanks to @Felix Kling for the jsPerf.)
因此，特别是对于闭包，只要你通过一些永久性保持闭包，就会有开销参考。我会说如果可能的话，尽量避免这种情况是好的，但不要过于强迫它。有时，添加到范围链中的新变量环境只是最佳解决方案。
So with respect to the closure in particular, yes there's overhead as long as you maintain the closure by some permanent reference. I'd say that it is good to avoid this if possible but not to be obsessive about it. Sometimes a new variable environment added to the scope chain is simply the best solution.
编辑： 这是Google的一篇文章。具体来说，请参阅使用闭包避免陷阱。有关扩展范围链的性能影响的信息，以及匿名函数比命名函数慢的声明。
Here's an article from Google. Specifically, see Avoiding pitfalls with closures. for information on the performance impact of extending the scope chain, and for a claim that anonymous functions are "slower" than named functions.
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