FnCall.js

// 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 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


/**
 * @param {Function} fn
 * @return {Function}
*/
// program


var once = function (fn) {
    let flag = false;
    return function (...args) {
        if (flag === false) {
            flag = true
            return fn(...args)
        } else {
            return undefined
        }
    }
};