可以用JavaScript生成函子吗?

我相信这就是你想要的:

var foo = (function () {
    var state = 0;

    return function () {
        return state++;
    };
})();

或者 the Wikipedia example :

var makeAccumulator = function (n) {
    return function (x) {
        n += x;
        return n;
    };
};

var acc = makeAccumulator(2);

alert(acc(2)); // 4
alert(acc(3)); // 7

JavaScript是其中一种语言,它作为一等公民对函数有着极好的支持。

由于Javascript函数是一流的对象,因此以下是实现此目的的方法:

var state = 0;
var myFunctor = function() { alert('I functored: ' + state++);};

这个 state myFunctor 函数的局部闭包。(本例中为全局)。这个问题的其他答案有更复杂的例子。

您可以将函数视为对象,并为它们指定“成员变量”。这里我们使用的是一个内部函数 fact ,而不是仅仅将其声明为局部变量( var loop = ... ),我们使用对象语法将其定义置于函数之外( fact.loop = ... ).这让我们基本上可以“导出”内部数据 loop 功能 以便该函数可以重用它 doubleFact

var fact = function(n) {
  return fact.loop(n, 1);
};

fact.loop = function(n, acc) {
  if (n < 1) {
    return acc;
  } else {
    return fact.loop(n-1, acc * n);
  }
};

var doubleFact = function(x) {
  return fact.loop(x * 2, 1);
};

console.log(fact(5)); // 120
console.log(doubleFact(5)); // 3628800

同样的想法也可以用来维持状态。

var countCalled = function() {
  console.log("I've been called " + (++countCalled.callCount) + " times.");
};

countCalled.callCount = 0;

countCalled(); // I've been called 1 times.
countCalled(); // I've been called 2 times.
countCalled(); // I've been called 3 times.

如果希望能够实例化多个,每个都有自己的状态,请尝试以下操作:

var CallCounter = function(name) {
  var f = function() {
    console.log(name + " has been called " + (++f.callCount) + " times.");
  };
  f.callCount = 0;
  return f;
};

var foo = CallCounter("foo");
var bar = CallCounter("bar");

foo();
foo();
bar();
foo();
bar();
bar();
bar();

console.log(foo.callCount);
console.log(bar.callCount);

产出:

foo has been called 1 times.
foo has been called 2 times.
bar has been called 1 times.
foo has been called 3 times.
bar has been called 2 times.
bar has been called 3 times.
bar has been called 4 times.
3
4

可以将闭包返回函数与附加的函数对象属性一起使用。 初始化后可以更改此类函子(闭包)的参数, 这在构建稍后可以运行/配置的计算时非常有用。看看下面的例子。这个答案类似于跛足黑猩猩。

function functor() {

  var run = function runX() {

    return runX.functorParam;

    // or: 

    // return run.functorParam;
  };

  run.functorParam = 'functor param'; // default value

  return run;
}

var f1 = functor();

// call f1
f1(); // 'functor param'


// lets change functor parameters:
f1.functorParam = 'Hello';


// call f1
f1(); // 'Hello'