Promise Time Limit – 2637

🔗LC2637 🟡 Medium 🧩 Pattern – Promises and Time

📅 Day 16/30 Days of JavaScript

Given an asynchronous function fn and a time t in milliseconds, return a new time limited version of the input function. fn takes arguments provided to the time limited function.

The time limited function should follow these rules:

• If the fn completes within the time limit of t milliseconds, the time limited function should resolve with the result.
• If the execution of the fn exceeds the time limit, the time limited function should reject with the string "Time Limit Exceeded".

Example

Input:
fn = async (n) => {
    await new Promise(res => setTimeout(res, 100));
    return n * n;

}

inputs = [5]
t = 50

Output:
{
    "rejected": "Time Limit Exceeded",
    "time": 50
}

Explanation:
const limited = timeLimit(fn, t)
const start = performance.now()
let result;
try {
    const res = await limited(...inputs)
    result = {
        "resolved": res,
        "time": Math.floor(performance.now() - start)
    };
} catch (err) {
    result = {
        "rejected": err,
        "time": Math.floor(performance.now() - start)
    };
}
console.log(result) // Output

The provided function is set to resolve after 100 ms.
However, the time limit is set to 50 ms.
It rejects at t = 50 ms because the time limit was reached.

Solution

/**
 * @param {Function} fn
 * @param {number} t
 * @return {Function}
 */

var timeLimit = function (fn, t) {
    const timeLimitedFunction = async (...args) => {
        // Rejects the promise after time t
        const rejectionTimerPromise = new Promise((resolve, reject) => {
            setTimeout(() => reject("Time Limit Exceeded"), t);
        });
        // async function promise - resolves if fn execution is complete and resolved
        const functionExecutionPromise = fn(...args);
        // Returns the first fulfilled promise i.e resolved or rejected first
        return Promise.race([functionExecutionPromise, rejectionTimerPromise]);
    }
    return timeLimitedFunction;
}

/**
 * const limited = timeLimit((t) => new Promise(res => setTimeout(res, t)), 100);
 * limited(150).catch(console.log) // "Time Limit Exceeded" at t=100ms
 */