javascript - 你能重置一个变量来存储调用包含闭包的函数的结果吗？

Question

是否可以重置调用包含闭包的函数的变量？在下面的示例中，这将是 counter。 (请注意，我是闭包的新手，所以一些评论可能是错误的。)

function makeCounter() {
 let count = 0;
 return function() {
   ++count;
   return `count equals ${count}`; 
 };
};

// If you just call it two times without storing the result in a variable, count is reset to zero each time
console.log(makeCounter()()); // count equals 1
console.log(makeCounter()()); // count equals 1

// Since the counter variable holds a reference to the result of the outer function's call (which is the inner returned function, which "closes over" count), the JavaScript engine won't wipe it from memory.
let counter = makeCounter();

// As expected, calling counter again updates it (storing the updated count value)
console.log(counter()); // count equals 1
console.log(counter()); // count equals 2 <-- Can you reset count as stored in counter?

Answer 1

使用该代码，不可能以任何方式重置 count 变量，这就是闭包的力量。

你可以做的是修改计数器，并实现一个方法reset

function makeCounter() {
 let count = 0;
 
 const counter = function() {
   ++count;
   return `count equals ${count}`; 
 }
 
 counter.reset = () => count = 0;
 
 return counter;
};

const counter = makeCounter();
console.log(counter());
console.log(counter());
counter.reset();
console.log(counter());

您还可以向该函数添加一个重置参数。

function makeCounter() {
    let count = 0;
    return function(reset) {
        if (reset)
            count = 0;
        ++count;
        return `count equals ${count}`;
    };
}