你能用 JavaScript 编写嵌套函数吗？
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Can you write nested functions in JavaScript?
提问by Red Swan
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（我在博客中读到它）。这真的可能吗？。事实上，我已经使用过这些，但我不确定这个概念。我对此真的不清楚 - 请帮忙！
回答by kennytm
Is this really possible.
这真的可能吗。
Yes.
是的。
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));回答by Quentin
The following is nasty, but serves to demonstrate how you can treat functions like any other kind of object.
以下内容令人讨厌，但用于演示如何像对待任何其他类型的对象一样对待函数。
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();
回答by cgp
Functions are first class objects that can be:
函数是第一类对象，可以是：
- Defined within your function
- Created just like any other variable or object at any point in your function
- Returned from your function (which may seem obvious after the two above, but still)
- 在您的函数中定义
- 就像在函数中的任何点创建的任何其他变量或对象一样
- 从您的函数返回（在上述两个之后似乎很明显，但仍然如此）
To build on the example given by Kenny:
以 Kenny 给出的示例为基础：
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.
会用 5 来提醒你。
回答by user3261767
Yes, it is possible to write and call a function nested in another function.
是的，可以编写和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(){
}
}
回答by Stefan Gruenwald
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:
您不仅可以返回作为变量传递给另一个函数的函数，还可以将其用于内部计算但在外部定义它。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
