index.ts

type JSONValue =
  | null
  | boolean
  | number
  | string
  | JSONValue[]
  | { [key: string]: JSONValue };
type OnceFn = (...args: JSONValue[]) => JSONValue | undefined;

/**
 * # 2666. Allow One Function Call
 * @link [LeetCode](https://leetcode.com/problems/allow-one-function-call/description/)
 *
 * @description
 * 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`.
 *
 * Constraints:
 * - calls is a valid JSON array
 * - 1 <= calls.length <= 10
 * - 1 <= calls[i].length <= 100
 * - 2 <= JSON.stringify(calls).length <= 1000
 *
 * @example
 * 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
 * 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
 *
 * @param {Function} fn
 * @returns {OnceFn}
 */
function once(fn: Function): OnceFn {
  let called = false;
  return function (...args) {
    if (called) return undefined;
    called = true;
    return fn(...args);
  };
}

/**
 * let fn = (a,b,c) => (a + b + c)
 * let onceFn = once(fn)
 *
 * onceFn(1,2,3); // 6
 * onceFn(2,3,6); // returns undefined without calling fn
 */

export { once };