函数对象和可调用对象有什么区别？ [英] What is the difference between a function object and a callable object?

问题描述

我最近看到演示文稿ECMAScript 5中的变化。并且有这个幻灯片声明：
$ b

功能 vs Callable

  typeof f ==='function'//→f是Callable 
（{}）。toString.call（f）==='[object函数]'//→f是函数
  

任何人都可以解释给我 和 Callable 之间的区别是什么？

一般来说，一个对象可以被调用而不是一个函数。在一切都是对象（包括函数）的语言中，可调用对象不必从Function类下降。

在JS中，它看起来像一个Callable任何具有[[Call]]内部方法的内容（由'function'类型标识，而不是'object'）。函数（如在幻灯片中使用的）是Function对象的后代。我可能是错的，但在脚本中，只能创建函数，而ECMAScript实现可以定义不是函数的Callables。

如果您尝试使用用匿名函数/函数表达式和声明函数滑动，结果是一样的。

// =='function'
（{}）。toString.call（function（）{}）// =='[object Function]'
function foo（）{}
typeof foo; // =='function'
（{}）。toString.call（foo）// =='[object Function]'

I recently saw the presentation about the changes in ECMAScript 5. And there was a slide with this statement:

Function vs Callable

typeof f === 'function'                       // → f is Callable
({}).toString.call(f) === '[object Function]' // → f is a Function

Can anyone explain to me what the difference between Function and Callable is?

解决方案

Generally speaking, an object can be callable without being a function. In a language where everything is an object (including functions), callable objects don't have to descend from a Function class.

In JS, it looks like a Callable is anything that has the internal [[Call]] method (identified by a typeof of 'function', as opposed to 'object'). A Function (as used in the slide) is a descendant of the Function object. I could be wrong, but within a script you can only create Functions while the ECMAScript implementation can define Callables that aren't Functions.

If you try the code fragment from the slide with both anonymous functions/function expressions and with declared functions, the results are the same.

typeof function() {}; // == 'function'
({}).toString.call(function() {}) // == '[object Function]'
function foo() {}
typeof foo; // == 'function'
({}).toString.call(foo) // == '[object Function]'

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