JavaScript, being one of the most popular programming languages, is a staple in web development. Whether you are a beginner or an experienced developer, preparing for a JavaScript interview can be daunting. This article aims to provide you with a comprehensive list of JavaScript interview questions that will help you ace your next interview. From basic syntax to advanced concepts, these questions will test your knowledge and understanding of JavaScript.
1. What is JavaScript?
JavaScript is a high-level, often just-in-time compiled language that conforms to the ECMAScript specification. It is primarily used for web development to create interactive web pages, but it can also be used for server-side programming with Node.js.
2. What is the difference between var, let, and const?
Var is function-scoped, let is block-scoped, and const is block-scoped but cannot be reassigned. Var is the oldest keyword for variable declaration, and let and const were introduced in ES6 (ECMAScript 2015) to provide better scoping and immutability.
3. What is hoisting?
Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope before code execution. However, only declarations are hoisted, not initializations.
4. What is the difference between == and ===?
== performs type coercion, which means it tries to convert the operands to the same type before comparing them. === performs strict equality, which means it compares the operands without type coercion.
5. What is a closure?
A closure is a function that has access to the outer function’s variables, even after the outer function has returned. It is created when a function is declared inside another function and has access to the outer function’s scope.
6. What is the difference between an array and an object in JavaScript?
An array is an ordered collection of elements, while an object is a collection of key-value pairs. Arrays are indexed, and objects are accessed using keys.
7. What is the difference between JSON and JavaScript object?
JSON (JavaScript Object Notation) is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. A JavaScript object is a more complex data structure that can contain functions, arrays, and other objects.
8. What is the difference between a prototype and a constructor?
A prototype is an object that is used to initialize newly created objects. A constructor is a function that is used to create and initialize objects of a class.
9. What is the difference between null and undefined?
Null is an assignment value that represents the intentional absence of any object value. Undefined is a type that indicates that a variable has been declared but has not yet been assigned a value.
10. What is the difference between a callback and a promise?
A callback is a function that is passed as an argument to another function and is executed after the outer function has completed its execution. A promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value.
These are just a few of the many JavaScript interview questions you might encounter. By understanding these concepts and practicing with more questions, you will be well-prepared to tackle any JavaScript interview. Good luck!
