3-23 请手动封装 fn(1)(2) 返回 3 的结果，要考虑参数会增加或减少的情况，例如：fn(1)(2)(3) 返回 6

https://juejin.cn/post/6850418115042836487
https://blog.csdn.net/double_sweet1/article/details/122786636?utm_medium=distribute.pc_aggpage_search_result.none-task-blog-2
https://blog.csdn.net/qq_35083721/article/details/119736941

方式一：递归 + 函数自定义属性

function cumulative(a) {
  let result = a ?? 0;
  let sum = function (...args2) {
    // 改造进行累加
    result = result += args2.reduce((cur, prv) => (cur += prv), 0);

    // 函数也是对象，可以给他添加属性
    sum.result = result;

    return sum;
  };
  // 怎么计算结果呢，args 里面存储着所有的值

  return sum;
}

console.log(cumulative(1)); // fn
console.log(cumulative(1)(2)); // fn
console.log(cumulative(1)(2)(3)); // fn
console.log(cumulative(1)(2)(3)(4)); // fn
console.log(cumulative(1)(2)(3)(4)(5)); // fn

// ====>
const res = cumulative(1)(2)(3)(4)(5);
console.log(res.result); // 15

方式二：递归 + 类型转换

function cumulative(...args) {
  let sum = function (...args2) {
    // 将参数存储到一起
    args.push(...args2);
    return sum;
  };

  // 怎么计算结果呢，args 里面存储着所有的值, 重写 toString
  sum.toString = function () {
    return args.reduce((cur, pre) => (cur += pre), 0);
  };

  return sum;
}

console.log(cumulative(1));
console.log(cumulative(1)(2));
console.log(cumulative(1)(2)(3));
console.log(cumulative(1)(2)(3)(4));
console.log(cumulative(1)(2)(3)(4)(5));

// ===>
const res = cumulative(1)(2)(3)(4)(5);
console.log(parseInt("" + res)); // 15

---

方式三：

const add = (a, b, c) => a + b + c;

const curry = (fn) => {
  let args = [];
  //返回一个函数
  return function temp(...newArgs) {
    args.push(...newArgs); //储存数据
    //数组长度和函数形参个数一致
    if (args.length === fn.length) {
      const val = fn.apply(this, args); //使用fn的方法添加数据
      args = [];
      return val; //返回最后添加的值
    } else {
      return temp;
    }
  };
};

const curryAdd = curry(add);

console.log(curryAdd(1)(2)(3)); // 6