JavaScript Interview Questions and Answers

What is JavaScript?

JavaScript is a high-level, interpreted programming language that is primarily used to add interactivity and dynamic behaviour to web pages. It is commonly used for client-side web development and can also be used for server-side development using frameworks like Node.js.

What are the key features of JavaScript?

Some key features of JavaScript include:

Dynamic typing: Variables can hold values of any data type without explicit declaration.

Prototype-based inheritance: Objects can inherit properties and methods from other objects.

First-class functions: Functions are treated as first-class citizens, allowing them to be passed around as arguments and returned from other functions.

Event-driven programming: JavaScript is well-suited for handling events such as user interactions and asynchronous operations.

Support for object-oriented, functional, and procedural programming paradigms.

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

The == operator checks for equality of values after performing type coercion, while the === operator checks for strict equality of values without type coercion. For example:

5 == '5' evaluates to true because the values are equal after type coercion.

5 === '5' evaluates to false because the values are of different types.

What is closure in JavaScript?

A closure is a function that retains access to variables from its parent scope even after the parent function has finished executing. Closures are created whenever a function is defined within another function and has access to variables from the outer function's scope.

Explain the concept of hoisting in JavaScript.

Hoisting is a JavaScript behaviour where variable and function declarations are moved to the top of their containing scope during the compilation phase. This means that variables and functions can be used before they are declared. However, only the declarations are hoisted, not the initializations.

What are arrow functions in JavaScript?

Arrow functions are a concise way to write anonymous functions in JavaScript. They provide a more compact syntax compared to traditional function expressions and lexically bind this value. For example:

These are just a few examples of JavaScript interview questions. Depending on the role and level of expertise required, interview questions can cover a wide range of topics including DOM manipulation, asynchronous programming, ES6 features, and more.