Allow One Function Call
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
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
/**
* @param {Function} fn
* @return {Function}
*/
var once = function(fn) {
let called = false; // flag to track if the function has been called
return function(...args) {
if (!called) {
called = true;
return fn.apply(this, args); // execute the function
} else {
return undefined; // return undefined for subsequent calls
}
};
};
let fn = (a, b, c) => a + b + c;
let onceFn = once(fn);
console.log(onceFn(1, 2, 3)); // Output: 6
console.log(onceFn(2, 3, 6)); // Output: undefined (without calling fn)