Mastering JavaScript Promises: A Guide for Interview Success
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Chapter 1: Introduction to Promises
As we embark on Day 58 of our 100 Days of JavaScript Interview Preparation, we delve into a key topic in JavaScript: Promises. This day marks a crucial segment of our learning journey, focusing on the distinctions between different types of promises in JavaScript.
In this video, "Mastering JavaScript - EVERYTHING You Need To Know," you will gain insights into the essential aspects of JavaScript, including promises and their significance in coding interviews.
Section 1.1: Key Promise Variants
Understanding the various promise methods is vital for mastering asynchronous JavaScript. Here’s a concise summary of the main promise methods:
- Promise.allSettled(): Waits for all promises to settle (either fulfilled or rejected).
- Promise.any(): Resolves when the first promise fulfills; if all are rejected, it returns an Aggregate Error.
- Promise.race(): Resolves as soon as the first promise settles (fulfills or rejects).
- Promise.all(): Waits for all promises to fulfill or for one to reject.
Section 1.2: Practical Examples
Let’s explore each method with simple code examples.
Subsection 1.2.1: Using Promise.allSettled()
const promises = [
Promise.resolve(1),
Promise.reject("Error!"),
Promise.resolve(3)
];
Promise.allSettled(promises)
.then(results => {
results.forEach(result => {
if (result.status === 'fulfilled') {
console.log('Fulfilled:', result.value);} else {
console.log('Rejected:', result.reason);}
});
});
This method is useful for scenarios where you want to wait for multiple asynchronous tasks to complete, regardless of their success or failure.
Subsection 1.2.2: Utilizing Promise.any()
const promises = [
Promise.reject("Error 1"),
Promise.resolve("Success!"),
Promise.reject("Error 2")
];
Promise.any(promises)
.then(value => {
console.log('Resolved:', value);})
.catch(error => {
console.log('All promises were rejected:', error);});
This approach is beneficial when only the fastest promise result is needed.
Subsection 1.2.3: Implementing Promise.race()
const promises = [
new Promise(resolve => setTimeout(() => resolve("Fastest"), 1000)),
new Promise(resolve => setTimeout(() => resolve("Slower"), 2000)),
new Promise(resolve => setTimeout(() => resolve("Slowest"), 3000))
];
Promise.race(promises)
.then(value => {
console.log('First resolved promise:', value);});
This method allows you to respond as soon as one of the promises completes, disregarding the others.
Chapter 2: Conclusion
In conclusion, mastering these promise methods is essential for any JavaScript developer, especially in interview scenarios. Each method serves a unique purpose, allowing for efficient handling of asynchronous operations.
In the video "JavaScript Interview Questions and Answers - Dominate Your Next Interview," you’ll find valuable tips and strategies to succeed in your coding interviews.
Happy coding, and remember to share your knowledge! Kindness and respect in the coding community go a long way. If you find this content helpful, please consider subscribing and supporting the journey!