README.md

2715. Timeout Cancellation

Description

Given a function fn, an array of arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.

After a delay of t, fn should be called with args passed as parameters unless cancelFn was invoked before the delay of t milliseconds elapses, specifically at cancelT ms. In that case, fn should never be called.

Example 1:

Input: fn = (x) => x * 5, args = [2], t = 20, cancelT = 50
Output:
[{"time": 20, "returned": 10}]
Explanation:
const cancel = cancellable((x) => x * 5, [2], 20); // fn(2)
called at t=20ms
setTimeout(cancel, 50);

The cancellation was scheduled to occur after a delay of cancelT (50ms), which happened after the execution of fn(2) at 20ms.

Example 2:

Input:
fn = (x) => x2, args = [2], t = 100, cancelT = 50
Output:
[]
Explanation:
const cancel = cancellable((x) => x2, [2], 100); // fn(2) not called
setTimeout(cancel, 50);

The cancellation was scheduled to occur after a delay of cancelT (50ms), which happened before the execution of fn(2) at 100ms, resulting in fn(2) never being called.

Example 3:

Input:
fn = (x1, x2) => x1 * x2, args = [2,4], t = 30, cancelT = 100
Output:
[{"time": 30, "returned": 8}]
Explanation:
const cancel = cancellable((x1, x2) => x1 * x2, [2,4], 30); // fn(2,4) called at t=30ms
setTimeout(cancel, 100);

The cancellation was scheduled to occur after a delay of cancelT (100ms), which happened after the execution of fn(2,4) at 30ms.

Constraints:

• fn is a function
• args is a valid JSON array
• 1 <= args.length <= 10
• 20 <= t <= 1000
• 10 <= cancelT <= 1000

Solution

1. 給定一個函數 fn、一個參數數組 args 和一個以毫秒為單位的超時 t，返回一個取消函數 cancelFn。

const cancellable = function(fn,args,t,cancelT){

    //setTimeout函數執行後會返回timeoutId
    let timeoutId = setTimeout(() => {
        fn(...args);
        console.log(`調用fn`);
    }, t);

    const cancelFn = ()=>{
        //clearTimeout(timeoutId);的用法
        clearTimeout(timeoutId);
    };    

    return cancelFn;
};

2. 測試 在延遲 t 毫秒之前（特別是在 cancelT ms 處）調用 cancelFn。

testcase1

const fn = (x) => x * 5;
const args = [2];
const t = 20;
const cancel = cancellable(fn, args, t); 

const cancelT = 50;

setTimeout(() => {
   cancel()
   console.log(`T1定時結束`) 
}, cancelT)

testcase2

//當 cancelT 小於 t 時，fn 不應該被調用

const fn2 = (x) => x * 5;
const args2 = [2];
const t2 = 100;
const cancel2 = cancellable(fn2, args2, t2); 

const cancelT2 = 50;

setTimeout(() => {
   cancel2();
   console.log(`T2定時結束`) ;
}, cancelT2)