JavaScript Interview Question #85

What is the difference between sequential and parallel asynchronous operations?

Promises, Async/Await, Fetch & Modern JavaScript Mid-Level Intermediate

Quick Interview Answer

Sequential code waits for one independent operation to finish before starting the next, increasing total latency. Parallel initiation starts independent operations before waiting for their combined results.

Detailed Explanation

When operations do not depend on one another, Promise.all is commonly used to await them concurrently. When one result is required before the next operation can even be constructed, sequential awaiting is appropriate.

Code Example

// Sequential
const user = await getUser();
const settings = await getSettings();

// Concurrent initiation
const [products, categories] = await Promise.all([
    getProducts(),
    getCategories()
]);