Allow One Function Call – 2666

🔗LC2666 🟢 Easy 🧩 Pattern – Function Transformations

📅 Day 10/30 Days of JavaScript

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.

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

Solution

/**
 * @param {Function} fn
 * @return {Function}
 */
var once = function (fn) {
    let isCalled = false
    return function (...args) {
        if (!isCalled) {
            isCalled = true;
            return fn(...args)
        }
        return undefined;
    }
};

/**
 * 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
 */