Implement an async function helper race() that executes multiple asynchronous functions concurrently and returns the result of the first function to complete, similar to Promise.race(). Unlike parallel(), it finishes as soon as any function completes or encounters an error.
Requirements
- Concurrent execution – Execute all async functions simultaneously
- First completion wins – Return the result of the first function to complete (success or error)
- Early termination – Stop and ignore remaining functions once first result is received
- Callback interface – Each async function follows the Node.js callback pattern
(error, data) => void
- Return async function –
race() should return a new async function that can be called
Key Behaviors
- Parallel execution – All functions start simultaneously and run concurrently
- First-wins semantics – Return the first result (success or error) and ignore the rest
- Immediate completion – Call final callback as soon as any function completes
- No result collection – Don't wait for or collect results from other functions
- Flexible input – Accept any number of async functions in the array
Example
const async1 = (callback) => {
setTimeout(() => callback(null, 1), 300);
};
const async2 = (callback) => {
setTimeout(() => callback(null, 2), 100);
};
const async3 = (callback) => {
setTimeout(() => callback(null, 3), 200);
};
const first = race([async1, async2, async3]);
first((error, data) => {
console.log(data); // 2, since async2 completes first
});
// Error handling
const asyncFail = (callback) => {
setTimeout(() => callback(new Error('Something failed')), 50);
};
const raceWithError = race([async1, asyncFail, async3]);
raceWithError((error, data) => {
console.log(error.message); // "Something failed"
console.log(data); // undefined
});
Key Challenge
The function must coordinate multiple concurrent async operations and return the first result (success or error) while ignoring all subsequent completions.