🔗LC2715 🟢 Easy 🧩 Pattern – Promises and Time
📅 Day 14/30 Days of JavaScript
Given a function fn, an array of arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.
After a delay of cancelTimeMs, the returned cancel function cancelFn will be invoked. setTimeout(cancelFn, cancelTimeMs)
Initially, the execution of the function fn should be delayed by t milliseconds. If, before the delay of t milliseconds, the function cancelFn is invoked, it should cancel the delayed execution of fn. Otherwise, if cancelFn is not invoked within the specified delay t, fn should be executed with the provided args as arguments.
Example
Input: fn = (x) => x * 5, args = [2], t = 20
Output: [{"time": 20, "returned": 10}]
Explanation:
const cancelTimeMs = 50;
const cancelFn = cancellable((x) => x * 5, [2], 20);
setTimeout(cancelFn, cancelTimeMs);
The cancellation was scheduled to occur after a delay of cancelTimeMs(50ms),
which happened after the execution of fn(2) at 20ms.Solution
If the timer setTimeout runs out the function is executed before that if cancelFn is called then the timer is cancelled and the function execution is stopped beforehand.
/**
* @param {Function} fn
* @param {Array} args
* @param {number} t
* @return {Function}
*/
var cancellable = function (fn, args, t) {
const timerId = setTimeout(fn, t, ...args);
const cancelFn = () => clearTimeout(timerId);
return cancelFn;
};
/** The code below explains how the solution can be tested
* const result = [];
*
* const fn = (x) => x * 5;
* const args = [2], t = 20, cancelTimeMs = 50;
*
* const start = performance.now();
*
* const log = (...argsArr) => {
* const diff = Math.floor(performance.now() - start);
* result.push({"time": diff, "returned": fn(...argsArr)});
* }
*
* const cancel = cancellable(log, args, t);
*
* const maxT = Math.max(t, cancelTimeMs);
*
* setTimeout(cancel, cancelTimeMs);
*
* setTimeout(() => {
* console.log(result); // [{"time":20,"returned":10}]
* }, maxT + 15)
*/