before

[Sunny-117]

before(num,fn)接受两个参数，第一个参数是数字，第二个参数是函数，调用before函数num次数以内，返回与fn执行相同的结果，超过num次数返回最后一次fn的执行结果。

[CXGBro]

function before(num, fn) {
  let count = 0
  let beforeNumRes
  return function (...args) {
    if (num > count) {
      beforeNumRes = fn(...args)
    }
    count += 1
    return beforeNumRes
  }
}

let func = before(3, (a, b) => a + b)
console.log(func(1, 2)); // 3
console.log(func(2, 3)); // 5
console.log(func(1, 6)); // 7
console.log(func(1, 8)); // 7

[bearki99]

function before(num, fn) {
  let cnt = 0;
  let ans;
  return function (...args) {
    if (num > cnt) {
      ans = fn(...args);
    }
    cnt++;
    return ans;
  };
}

闭包应用

[veneno-o]

// 本来想试试迭代器,不过用现闭包才是正解
function before(num, callback){
    let res;
    return function (...args){
        if(num-- > 0){
            res = callback(...args)
            return res;
        }
        return res;
    }
}

[kangkang123269]

function before(num, fn) {
    let count = 0;
    let lastResult;
    return function(...args) {
        if (count < num) {
            lastResult = fn.apply(this, args);
            count++;
        }
        return lastResult;
    };
}

let testFn = function(x) { return x * x; };
let beforeTestFn = before(3, testFn);

console.log(beforeTestFn(2)); // 输出 4
console.log(beforeTestFn(3)); // 输出 9
console.log(beforeTestFn(4)); // 输出 16
console.log(beforeTestFn(5)); // 输出 16，因为已经超过了3次调用，所以返回最后一次执行结果。