What Are Interview Questions For JavaScript?

Frequently Asked Questions: Interview Questions for JavaScript

1. What are the key features of JavaScript? JavaScript is a versatile programming language with several key features, including:

   • It is a lightweight scripting language.
   • It is interpreted and runs on the client-side.
   • It supports event-driven, functional, and object-oriented programming paradigms.
   • It provides dynamic typing and automatic memory management.

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

   • null represents the intentional absence of any object value.
   • undefined indicates that a variable has been declared but has not been assigned any value. It is also the default value of uninitialized variables.

3. Explain the concept of hoisting in JavaScript. Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase. This allows you to use variables and functions before they are declared in your code.

4. What are closures in JavaScript? Closures are functions that have access to variables from their outer (enclosing) function scope, even after the outer function has finished executing. They "remember" the environment in which they were created.

5. What is the purpose of the this keyword in JavaScript? The this keyword refers to the object on which a function is currently being executed. Its value is determined by how the function is called. It allows you to access and manipulate properties within the object's scope.

6. What is event delegation in JavaScript? Event delegation is a technique where a single event handler is attached to a parent element instead of attaching individual handlers to multiple child elements. Events that occur on child elements will "bubble up" to the parent element, allowing you to handle them centrally.

7. What is the difference between let, const, and var in JavaScript?

   • var is function-scoped and can be redeclared and reassigned within its scope.
   • let and const are block-scoped and cannot be redeclared in the same scope. However, let allows reassignment, whereas const does not.

8. How does prototypal inheritance work in JavaScript? JavaScript uses prototypal inheritance, where objects can inherit properties and methods from other objects. Each object has an internal link to another object called its prototype. If a property or method is not found in the current object, JavaScript looks for it in the prototype chain until it reaches the root object.

9. What are the differences between == and === in JavaScript?

   • == is a loose equality operator that compares values after performing type conversions if necessary.
   • === is a strict equality operator that compares values without performing type conversions. It checks for both value and type equality.

10. What is the purpose of the async and await keywords in JavaScript? async and await are used to handle asynchronous operations in a more synchronous-looking way. The async keyword is used to define an asynchronous function, and await is used to pause the execution of an async function until a promise is fulfilled or rejected.

These are just a few commonly asked interview questions for JavaScript. Remember to practice and understand the concepts thoroughly to perform well in your interviews.