JavaScript Mock Interview | Interview Questions for Senior JavaScript Developers | Part 1

Summary

This video features a mock interview session for an experienced JavaScript developer position. The interviewer, José, and the candidate, Lao, discuss various JavaScript concepts, including single-threaded execution, asynchronous operations, promises, event loops, and optimizations like memoization and web workers. Lao shares his professional experience with frameworks like React and Node.js and highlights past projects, such as a website builder and an inventory management system. The video also delves into the differences between JavaScript functions like `call` and `apply`, and objects like `Map` and `WeakMap`. Viewers are encouraged to comment if they want a part two.

Takeaways

• 🎤 The host, Jose, from Montreal, Canada, is conducting a mock interview for an experienced JavaScript developer role.
• 💻 Lao, the interviewee, has 4-4.5 years of experience working with JavaScript and frameworks like Node.js, Express.js, and React.js.
• 🌐 Lao describes an interesting project where he built a website builder with drag-and-drop functionality for easy user deployment.
• 📊 Another project Lao worked on involved an inventory management system that predicted future sales for better production planning.
• 🧵 JavaScript is single-threaded but can handle asynchronous operations using the event loop, promises, and timers.
• ⚙️ Lao explains the difference between `Promise.all` (which rejects all promises if one fails) and `Promise.allSettled` (which resolves all promises regardless of failure).
• 🔄 Event emitters in JavaScript can be used to trigger custom events and allow for subscribing or unsubscribing to certain actions.
• 🚀 Optimization techniques mentioned by Lao include memoization, caching, using `break` and `continue`, and avoiding memory leaks.
• 🛠️ Lao discusses the differences between `call` (arguments passed separately) and `apply` (arguments passed as an array) in JavaScript.
• 🔑 Lao also highlights the difference between `Map` (stores key-value pairs and is iterable) and `WeakMap` (stores object references and is not iterable, allowing for garbage collection).

Q & A

What is the professional background of the interviewer, Jose?

Jose is a technical tutor with over 17 years of experience. His expertise lies in JavaScript, and he works on hiring engineers by helping with the vetting process. He is from Montreal, Canada.

What JavaScript frameworks and libraries has the interviewee, Lao, worked with?

Lao has worked with several JavaScript frameworks and libraries, including Node.js, Express.js, Next.js for backend, and React.js for frontend development. He also used UI libraries like Material-UI, Ant Design, and Chakra UI.

Can you describe one of the interesting JavaScript projects that Lao has worked on?

Lao worked on a website builder project where users could drag and drop elements to create a website. It also featured a deployment process that allowed users to assign a domain and publish their website with a single click.

How does JavaScript handle asynchronous operations like promises and timers?

JavaScript handles asynchronous operations using an event loop. It manages a call stack and an event queue. Asynchronous tasks like promises or timers are pushed to the event queue, and once the main thread is clear, the event loop picks them up and executes their callbacks.

What is the difference between promises and observables in JavaScript?

A promise handles a single event and can either be resolved or rejected, while an observable is used for multiple events and works with subscribers. Observables allow multiple values over time, whereas promises deal with one-time results.

What is the difference between Promise.all and Promise.allSettled?

Promise.all rejects as soon as one of the promises in the array rejects, while Promise.allSettled waits for all promises to complete and returns an array with the results of each promise, whether they were fulfilled or rejected.

What are event emitters in JavaScript?

Event emitters allow functions to manually trigger events and notify listeners that certain actions have occurred. It works on a publisher-subscriber model, where subscribers listen for events, and when an event is emitted, the associated callback functions are executed.

What are some optimization techniques in JavaScript mentioned by Lao?

Some optimization techniques include caching or memoization of function return values, using break and continue in loops to reduce unnecessary iterations, using web workers for background tasks, and avoiding memory leaks by clearing intervals and using function-scoped variables.

What is the difference between the call and apply methods in JavaScript?

The call method accepts arguments separately, while the apply method takes arguments as an array. Both are used to invoke a function with a specific 'this' context, but apply is useful when you have an array of arguments.

What is the difference between a map and a weak map in JavaScript?

A map holds key-value pairs, where the keys can be of any type, and the values persist in memory until explicitly removed. A weak map only allows objects as keys and holds references to those keys, which can be garbage-collected once they are no longer referenced elsewhere in the code.