Javascript Interview Questions & Answers For Your Interview

Team IndisJobJanuary 12, 2024Last Updated: January 12, 2024

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Java is a widely used programming language famous for creating enterprise, web, and mobile applications. Java is also used for creating server-side applications, desktop applications, and games. Java interview questions can cover various topics, from basic programming concepts to advanced Java frameworks.

Top 25 Javascript Interview Questions & Answers

Check here our top 25 Javascript Interview Questions and Answers:

What is JavaScript, and what are its features?

JavaScript is a high-level, object-oriented programming language. Its features include dynamic typing, first-class functions, event-driven programming, and prototypal inheritance.

What is the difference between “undefined” and “null” in JavaScript?

Undefined means a variable has been declared but has not yet been assigned a value, while null is an assignment value that represents no value or no object.

What is the difference between “==” and “===” in JavaScript?

“==” compares the value of two operands, while “===” compares the value and data type of the operands.

What is “hoisting” in JavaScript?

Hoisting is a mechanism in JavaScript where variables and function declarations are moved to the top of their respective scopes during the compilation phase.

What is a closure in JavaScript?

A closure is a function that has access to the variables in its outer part, even after the external process has returned.

What is the difference between a function declaration and a function expression in JavaScript?

A function declaration is hoisted to the top of its scope and can be called before it is defined, while a function expression is not boosted and can only be called after it has been determined.

What is “this” keyword in JavaScript?

The “This” keyword refers to the object of which the function is a method.

What are the different ways to create an object in JavaScript?

There are several ways to create an object in JavaScript, including object literals, constructor functions, and the Object.create() method.

What is event bubbling in JavaScript?

Event bubbling is a process in which an event is triggered on a child element and then bubbles up through the parent elements in the DOM tree until it reaches the document object.

What is the difference between “let” and “var” in JavaScript?

“Let” is block-scoped, while “var” is function-scoped. This means that variables declared with “let” are only accessible within the block defined in, while variables declared with “var” are accessible within the entire function they were limited in.

What is a callback function in JavaScript?

A callback function is a function that is passed as an argument to another position and is executed after that function has been completed.

What is the difference between synchronous and asynchronous programming in JavaScript?

Synchronous programming executes code sequentially, while asynchronous programming allows code to run concurrently.

What is the “prototype” property in JavaScript?

The “prototype” property is a mechanism in JavaScript that allows objects to inherit properties and methods from their parent objects.

What is the “bind” method in JavaScript?

The “bind” method creates a new function with a specified “this” keyword and any arguments passed to it.

What is the difference between “slice” and “splice” in JavaScript?

“Slice” creates a new array that contains a portion of the original array, while “splice” modifies the original collection by removing or adding elements to it.

What is the “spread” operator in JavaScript?

The “spread” operator allows an iterable object, such as an array or a string, to be expanded into individual elements.

What is the difference between “map” and “forEach” in JavaScript?

“Map” creates a new array with the results of calling a function on each element of the original collection, while “forEach” executes a process on each part of the original array.

What is the “Promise” object in JavaScript?

The “Promise” object is a mechanism in JavaScript that allows asynchronous operations and returns a value once the process is complete.

What are the different types of operators in JavaScript?

JavaScript supports several types of operators, including arithmetic operators (+, -, *, /), comparison operators (>, <, >=, <=), logical operators (&&, ||, !), assignment operators (=, +=, -=, *=, /=), and others.

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

Var is function-scoped, while let and const are block-scoped. Var can be redeclared and reassigned, let can be reassigned but not redeclared, and const cannot be reassigned or redeclared.

What is a closure in JavaScript?

A closure is a function that has access to the variables defined in its outer scope, even after that scope has closed.

What is the event loop in JavaScript?

The event loop is a mechanism that allows JavaScript to perform non-blocking I/O operations. It handles events and callbacks and ensures that the execution of JavaScript code never blocks the main thread.

What is asynchronous programming in JavaScript?

Asynchronous programming in JavaScript involves executing code without blocking the main thread. This is typically done using callbacks, promises, or async/await.

What is the purpose of the ‘this’ keyword in JavaScript?

The ‘this’ keyword refers to the object currently executing the function. Its value depends on how the process is called and can be changed using the call(), apply(), and bind() methods.