你能用JavaScript编写嵌套函数吗？

I am wondering if JavaScript supports writing a function within another function, or nested functions (I read it in a blog). Is this really possible?. In fact, I have used these but am unsure of this concept. I am really unclear on this -- please help!

我想知道JavaScript是否支持在另一个函数或嵌套函数中编写函数（我在博客中阅读它）。这真的有可能吗？事实上，我已经使用过这些但不确定这个概念。我真的不清楚 - 请帮忙！

5 个解决方案

#1

151

Is this really possible.

这真的有可能吗？

Yes.

是。

function a(x) {    // <-- function
  function b(y) { // <-- inner function
    return x + y; // <-- use variables from outer scope
  }
  return b;       // <-- you can even return a function.
}
console.log(a(3)(4));

#2

The following is nasty, but serves to demonstrate how you can treat functions like any other kind of object.

以下是讨厌的，但用于演示如何处理像任何其他类型的对象一样的函数。

var foo = function () { alert('default function'); }

function pickAFunction(a_or_b) {
    var funcs = {
        a: function () {
            alert('a');
        },
        b: function () {
            alert('b');
        }
    };
    foo = funcs[a_or_b];
}

foo();
pickAFunction('a');
foo();
pickAFunction('b');
foo();

#3

Functions are first class objects that can be:

函数是第一类对象，可以是：

Defined within your function
在你的功能中定义
Created just like any other variable or object at any point in your function
在函数的任何位置创建就像任何其他变量或对象一样
Returned from your function (which may seem obvious after the two above, but still)
从您的函数返回（在上面的两个之后可能看起来很明显，但仍然）

To build on the example given by Kenny:

以Kenny给出的例子为基础：

   function a(x) {
      var w = function b(y) {
        return x + y;
      }
      return w;
   };

   var returnedFunction = a(3);
   alert(returnedFunction(2));

Would alert you with 5.

用5提醒你。

#4

Yes, it is possible to write and call a function nested in another function.

是的，可以编写并调用嵌套在另一个函数中的函数。

Try this:

尝试这个：

function A(){
   B(); //call should be B();
   function B(){

   }
}

#5

Not only can you return a function which you have passed into another function as a variable, you can also use it for calculation inside but defining it outside. See this example:

您不仅可以将已传递给另一个函数的函数作为变量返回，还可以将其用于计算内部但在外部定义。看这个例子：

    function calculate(a,b,fn) {
      var c = a * 3 + b + fn(a,b);
      return  c;
    }

    function sum(a,b) {
      return a+b;
    }

    function product(a,b) {
      return a*b;
    }

    document.write(calculate (10,20,sum)); //80
    document.write(calculate (10,20,product)); //250

#1

151