However, excelling in interviews is not the only aspect. Understanding closures and asynchronous programming is crucial for becoming an effective and confident developer.
Imagine you’re building a weather application. You can’t halt the entire app to fetch weather data. Here, asynchronous programming methods like callbacks, promises, and async/await come to your rescue.
Question: What is ‘callback hell’ in the context of using callbacks, and what are its disadvantages?
Answer: “Callback hell” is used when you have many nested callbacks in our code. Think of it as a layer cake of functions where each layer depends on the one above it. This makes our code look like a pyramid, often called the “Pyramid of Doom.” The downside? It makes our code hard to read and even harder to debug. Plus, each new layer adds complexity, making future changes a headache.
Question: How is a Promise different from a callback, and what are the three states of a Promise?
Answer: Promises to improve upon callbacks by offering better code readability and easier error handling. A Promise can be in one of three states: pending, fulfilled, or rejected.
Question: How does async/await help in writing asynchronous code?
Answer: Async/await makes our code easier to read and write. It’s based on Promises but looks like traditional synchronous code.
2. Advanced Array Methods
When dealing with arrays, methods like
reduce are your best friends. These methods can be beneficial in scenarios like sorting and filtering products on an e-commerce website.
// Example using map const numbers = [1, 2, 3]; const squared = numbers.map(x => x * x);
Question: Briefly overview the
map method transforms each item into an array and produces a new array of the same length. The
filter method returns a new array containing only items that pass a specified condition. The
reduce method processes each element in the array with an accumulator to reduce the array to a single value.
Closures are unique types of functions that allow for data hiding and encapsulation. They can be extremely useful in scenarios such as user authentication, where you may want to create private variables.
Question: What is a closure, and how can it be used to create private data?
Answer: Consider closure as a function that can “remember” its outer scope, enabling you to create variables that are not accessible externally. This capability makes closures invaluable for data hiding and encapsulation.
this keyword is essential for manipulating object data and working with event handlers. Its value can change based on the context in which it’s used.
Question: How does
apply() explicitly set its value.
5. Prototypal Inheritance
For example, if you’re developing a game, you might have different enemies that share some traits but also have unique abilities. With prototypal inheritance, managing this kind of complexity becomes easy.
6. ES6 Features
Answer: Destructuring lets you unpack values from arrays or objects into distinct variables. It makes code cleaner and easy to understand.
Answer: The spread operator unfolds array elements or object properties. The rest operator does the opposite: it gathers elements into a new array or object.
7. Error Handling
Errors are inevitable in programming. Understanding how to handle them gracefully can significantly impact user experience.
// Example of throwing a custom error throw new Error("This is a custom error");
Answer: The try-catch block allows developers to test a block of code for errors. If an error occurs in the try block, the code can jump to the catch block without crashing the application.
Answer: Custom errors can be created using the throw statement, which allows you to define your error messages and types.
8. Event Delegation
Question: Why is event delegation beneficial, and how does it work?
Answer: Event delegation allows setting an event listener on parent rather than child elements. It takes advantage of the fact that events bubble up the DOM. This improves performance and ensures that dynamically added elements will still trigger the event.
9. Module Patterns
Question: How can you use the import and export statements in ES6?
Answer: ES6 lets us break our code into modules. We can export and import variables, functions, or objects in other files. This helps in code organization and reuse.
10. Throttling and Debouncing
Question: What are throttling and debouncing, and why are they essential in event handling?
Answer: Throttling and debouncing are performance techniques. Throttling allows a function to run only once in a set time. Debouncing delays the function until a certain time has passed since the last call.
11. Web Storage
Deciding where and how to store data is crucial when creating a web application. This is where localStorage and sessionStorage come into play.
Question: How do
localStorage persists data even when the browser is closed and reopened, making it suitable for long-term storage. On the other hand,
sessionStorage only keeps data for the duration of the page session.
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