10 common javascript interview questions

June 30, 2023

Preparing for a JavaScript interview can be an exciting yet nerve-wracking experience. Whether you're a seasoned developer or just starting your journey, having a solid understanding of JavaScript is crucial. In this blog post, we'll explore 10 common JavaScript interview questions and provide detailed answers to help you prepare for your next interview. So, let's dive in and get ready to ace those technical interviews!

 1. What is JavaScript and what are its key features? 

    JavaScript is a high-level, interpreted programming language primarily used for adding interactivity to web pages. It has several key features, including being lightweight, object-oriented, and supporting event-driven programming. Read more...

2. What is the difference between null and undefined in JavaScript? 

    null represents the intentional absence of any object value, while undefined indicates that a variable has been declared but has not been assigned a value. null is a value that can be assigned to a variable, whereas undefined is the default value when a variable is declared but not initialized. Read more...

3. How does JavaScript handle asynchronous programming? 

   JavaScript handles asynchronous programming through mechanisms such as callbacks, Promises, and async/await. These allow non-blocking execution of code, enabling functions to run in the background while other operations are being performed. Read more...

4. What are closures in JavaScript and how do they work? 

    A closure is an inner function that has access to its own scope, the scope of its outer function, and the global scope. It retains access to these variables even after the outer function has finished executing. Closures are created when an inner function is returned or passed as an argument to another function. Read more...

5. What is the purpose of the this keyword in JavaScript? 

    The this keyword refers to the current context or object on which a function is being executed. Its value is determined by how a function is invoked and can vary. In the global scope, this refers to the global object (e.g., window in a browser). Inside an object method, this refers to the object itself. Read more...

6. Explain the concept of prototypal inheritance in JavaScript.:

    Prototypal inheritance is a mechanism in JavaScript where objects can inherit properties and methods from other objects. Every object in JavaScript has an associated prototype object, and if a property or method is not found on the object itself, it is looked up in the prototype chain. Read more...

7. What is the event loop in JavaScript and how does it work?

    The event loop is a mechanism in JavaScript that handles asynchronous callbacks and ensures that they are executed in the correct order. It continuously checks the call stack for functions to execute and processes events from the event queue, executing callbacks as appropriate. Read more...

8. How does hoisting work in JavaScript?

    Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their respective scopes during the compilation phase, before the code is executed. This allows variables to be used before they are declared, although it's considered best practice to declare variables before using them. Read more...

9. Explain the concept of callbacks and provide an example of their usage.:

    Callbacks are functions that are passed as arguments to other functions and are invoked once a particular operation is complete. They are commonly used in asynchronous programming, event handling, and for executing code after a certain task finishes.

10. What are some methods to handle errors in JavaScript? 

    There are several error-handling mechanisms in JavaScript, including try-catch statements, the throw statement for manually throwing errors, and the use of Error objects to create custom error types. Additionally, async functions can use the try-catch blocks or catch method to handle errors.

 Extra question: Is javascript a single thread language?

   Yes, JavaScript is often described as a single-threaded language. This means that it executes one piece of code at a time in a single sequence, following a specific order. However, it's important to note that JavaScript also has mechanisms for handling asynchronous operations, such as callbacks, Promises, and async/await, which allow non-blocking execution and can give the impression of concurrency.
In summary, although JavaScript itself is single-threaded, its asynchronous nature allows it to handle concurrent tasks by leveraging mechanisms like callbacks and event-driven programming.

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