# 2666. Allow One Function Call

###### tags: `leetcode 30 days js challenge` `Easy`

[2666. Allow One Function Call](https://leetcode.com/problems/allow-one-function-call/)

### 題目描述

Given a function `fn`, return a new function that is identical to the original function except that it ensures `fn` is called at most once.

- The first time the returned function is called, it should return the same result as `fn`.
- Every subsequent time it is called, it should return `undefined`.

### 範例

**Example 1:**

Input: fn = (a,b,c) => (a + b + c), calls = [[1,2,3],[2,3,6]]
Output: [{"calls":1,"value":6}]
Explanation:
const onceFn = once(fn);
onceFn(1, 2, 3); // 6
onceFn(2, 3, 6); // undefined, fn was not called

**Example 2:**

Input: fn = (a,b,c) => (a * b * c), calls = [[5,7,4],[2,3,6],[4,6,8]]
Output: [{"calls":1,"value":140}]
Explanation:
const onceFn = once(fn);
onceFn(5, 7, 4); // 140
onceFn(2, 3, 6); // undefined, fn was not called
onceFn(4, 6, 8); // undefined, fn was not called

**Constraints**:

- `1 <= calls.length <= 10`
- `1 <= calls[i].length <= 100`
- `2 <= JSON.stringify(calls).length <= 1000`

### 解答

#### TypeScript

function once<T extends (...args: any[]) => any>(
  fn: T
): (...args: Parameters<T>) => ReturnType<T> | undefined {
  let hasBeenCalled = false;
  return (...args) => {
    if (hasBeenCalled) return;
    hasBeenCalled = true;
    return fn(...args);
  };
}

> [name=Sheep][time=Fri, May 12, 2023]

### Reference

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