Important Concepts

Question 1

What is a variable in JavaScript?

Answer 1

A variable is a container that holds a value. It is used to store and manipulate data in a program.

Question 2

What is a function in JavaScript?

Answer 2

A function is a reusable block of code that is used to perform a specific task. Functions can take input and return output.

Question 3

What is an object in JavaScript?

Answer 3

An object is a fundamental concept in JavaScript that allows you to store properties and methods in a single unit. Objects are defined using curly braces {} and can have properties and methods that can be accessed using dot notation.

Question 4

What is an Array in JavaScript?

Answer 4

An array is a special kind of object that can hold multiple values in a single variable. The values are stored in a linear fashion and can be accessed by their index.

Question 5

What is a Conditional Statement in JavaScript?

Answer 5

Conditional statements allow you to specify different actions to be taken depending on certain conditions. if-else and switch statement are the examples of Conditional statements.

Question 6

What is a Loop in JavaScript?

Answer 6

A loop is a control flow statement that allows you to execute a block of code multiple times. for, for-in, for-of and while are examples of loops in javascript.

Question 7

What is a constructor function in JavaScript?

Answer 7

A constructor function is a special kind of function that is used to create new objects. Constructor functions are invoked with the “new” keyword and are usually used to set the initial state of an object.

Question 8

What are Prototypes in JavaScript?

Answer 8

A prototype is an object that is used as a template for creating new objects. It is a mechanism that allows objects to inherit properties and methods from another object.

Question 9

What is closure in JavaScript?

Answer 9

A closure is a function that has access to variables in its parent scope even after the parent function has returned. Closure allows to create private variables, and to create stateful functions.

Question 10

What is a Promises in JavaScript?

Answer 10

A promise is an object that represents the eventual completion (or failure) of an asynchronous operation and its resulting value. Promises allow you to write asynchronous code that is easier to read and debug.

Question 11

What is Event Loop in JavaScript?

Answer 11

The event loop is a mechanism that handles the execution of code in JavaScript. It is responsible for determining when to execute callback functions, and it allows the JavaScript runtime to run multiple tasks in parallel.

Question 12

What is Asynchronous JavaScript?

Answer 12

Asynchronous JavaScript refers to the ability of JavaScript to handle multiple tasks at the same time. It allows your code to run without getting blocked, so the web page remains responsive, and multiple tasks can be handled simultaneously.

Question 13

What is hoisting in JavaScript?

Answer 13

Hoisting is a mechanism in JavaScript where variable and function declarations are moved to the top of the scope, regardless of where they appear in the code. This can lead to unexpected behavior if not handled properly.

Question 14

What is the keyword this in JavaScript?

Answer 14

The keyword this refers to the object that the code is currently being executed in. Its value can change depending on the context in which it is used.

Question 15

What is try-catch block in JavaScript?

Answer 15

The try-catch block is a way to handle errors that might occur in a program. It works by allowing you to place your code in a try block, and if an error occurs, it will be caught in the catch block, where you can take appropriate action.

Question 16

What are Regular Expressions in JavaScript?

Answer 16

Regular expressions are a way to search and match patterns in strings. They are defined using the RegExp constructor and can be used to perform tasks such as validation, pattern matching, and string replacement.

Question 17

What is an Immediately-Invoked Function Expression (IIFE) in JavaScript?

Answer 17

An IIFE, or Immediately-Invoked Function Expression, is a function that is immediately invoked after it is defined. It allows you to create a scope for variables and functions, effectively hiding them from the rest of the code.

Question 18

What is a generator function in JavaScript?

Answer 18

A generator function is a special kind of function that can be paused and resumed. It uses the keyword yield to indicate where the function should be paused and resumed. This allows writing asynchronous code in a more synchronous style.

Question 19

What is JSON in JavaScript?

Answer 19

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. JSON is a standard format for data exchange between a browser and a server.

Question 20

what is AJAX in JavaScript?

Answer 20

AJAX (Asynchronous JavaScript and XML) is a technology that allows you to send and receive data from a server asynchronously, without reloading the entire page. It is used to build dynamic and responsive web applications.

Question 21

What is a webpack in JavaScript?

Answer 21

webpack is a JavaScript module bundler. It allows bundling all the js files, CSS, and other resources used in the web application. It can bundle, minify, and optimize the files making the web application run faster and more optimized.

Question 22

What is Lazy Loading in JavaScript?

Answer 22

Lazy loading is a technique that defers the loading of resources until they are actually needed. This can improve the performance of a web application by reducing the amount of data that needs to be loaded up front.

Question 23

What is a Virtual DOM in JavaScript?

Answer 23

Virtual DOM is a lightweight in-memory representation of the actual Document Object Model (DOM) that allows to efficiently update the UI, by only updating the actual DOM nodes that have changed.

Question 24

What is the difference between let and var in JavaScript?

Answer 24

let and var are used for variable declaration in JavaScript, but there are some key differences. let has a block scope and the variable is not accessible outside the block it is declared in, while var has a function scope and the variable is accessible throughout the entire function.

Question 25

What is the spread operator in JavaScript?

Answer 25

The spread operator (…) allows you to expand an iterable (e.g. an array or a string) into its individual elements. It can be used to create a new array or to merge multiple arrays.

Question 26

What are default parameters in JavaScript?

Answer 26

Default parameters are a feature of JavaScript that allows you to specify default values for function parameters. This means that if a value is not passed for a particular parameter, the default value will be used instead.

Question 27

What is a Map in JavaScript?

Answer 27

A Map is a collection of key-value pairs. It is a built-in object that allows you to easily store, access, and update data. Maps are similar to objects, but they have some additional functionality and are more efficient for certain use cases.

Question 28

What is a Set in JavaScript?

Answer 28

A Set is a collection of unique values. It is a built-in object that allows you to easily store, access, and update data. Sets are similar to arrays, but they only store unique values and are more efficient for certain use cases.

Question 29

What is a Symbol in JavaScript?

Answer 29

A Symbol is a unique, immutable data type that can be used as a property key. It can be used to create object properties that can’t be accessed using string keys.

Question 30

What is Destructuring in JavaScript?

Answer 30

Destructuring is a feature of JavaScript that allows you to extract values from arrays or objects into individual variables. It can be used to simplify code by making it more readable and less verbose.

Question 31

What is a Class in JavaScript?

Answer 31

A class is a blueprint for creating objects. Classes allow you to create objects with the same properties and methods and they can be used to define a contract that an object should follow.

Question 32

What is the spread operator in JavaScript?

Answer 32

The spread operator (…) allows you to expand an iterable (e.g. an array or a string) into its individual elements. It can be used to create a new array or to merge multiple arrays.

Question 33

What is Async/Await in JavaScript?

Answer 33

Async/Await is JavaScript keywords that allow you to write asynchronous code in a more synchronous-looking way, making it easier to read and understand. It allows you to write asynchronous code using synchronous code syntax.

Question 34

What is a Ternary operator in JavaScript?

Answer 34

The ternary operator is a shorthand way of writing an if-else statement in JavaScript. It can be used to test a condition and return a value based on the outcome.

Question 35

What is Event Bubbling in JavaScript?

Answer 35

Event bubbling is a mechanism that allows events to be propagated up the DOM tree. It happens when an event is triggered on a child element

Question 36

What is Event Capturing in JavaScript?

Answer 36

Event capturing is a mechanism that allows events to be propagated down the DOM tree. It happens before the event reaches the target element and it can be used to track events at the top level of the DOM tree.

Question 37

What is Event Delegation in JavaScript?

Answer 37

Event delegation is a technique where an event handler is attached to a parent element and it (the event handler) listens to the events on its child elements. It allows for avoiding adding event listeners to individual elements and reduces the number of event listeners that need to be managed.

Question 38

What is the bind() method in JavaScript?

Answer 38

The bind() method creates a new function that, when called, has its ‘this’ keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called. It allows calling a function with a specific this value.

Question 39

What is the call() method in JavaScript?

Answer 39

The call() method calls a function with a given this value and arguments provided individually. It allows calling a function with a specific this value and individual arguments.

Question 40

What is the apply() method in JavaScript?

Answer 40

The apply() method calls a function with a given this value and arguments provided as an array. It allows calling a function with a specific this value and an array of arguments.

Question 41

What is a WeakMap in JavaScript?

Answer 41

A WeakMap is a collection of key-value pairs, similar to a Map, but its keys must be objects and the references to the keys are held weakly, allowing them to be garbage collected if there are no other references to them.

Question 42

What is a WeakSet in JavaScript?

Answer 42

A WeakSet is a collection of unique values, similar to a Set, but the references to its values are held weakly, allowing them to be garbage collected if there are no other references to them.

Question 43

What is a Currying in JavaScript?

Answer 43

Currying is a technique of breaking down a function that takes multiple arguments into a sequence of functions that each take a single argument. This can make the code more reusable and composable.

Question 44

What is a Recursion in JavaScript?

Answer 44

Recursion is a technique of calling a function from within itself until a certain condition is met. It can be useful for solving problems that can be broken down into smaller sub-problems.

Question 45

What is a Higher-Order Function in JavaScript?

Answer 45

A higher-order function is a function that takes one or more functions as arguments or returns a function as its result. It allows abstract functionality and writing more flexible and reusable code.

Question 46

What is a Composition in JavaScript?

Answer 46

Composition is a technique of combining small, single-purpose functions to create more complex functionality. It allows for building more complex functionality by composing simple functions together.

Question 47

What is a Partial Application in JavaScript?

Answer 47

Partial application is a technique of creating a new function by pre-filling some of the arguments of an existing function. It allows the creation of specialized versions of a function that are tailored to specific use cases.

Question 48

What is a Transpilation in JavaScript?

Answer 48

Transpilation is the process of converting code written in one programming language to another, often to a more compatible version. It allows using modern language features even in environments that don’t support them.

Question 49

What is a Proxy in JavaScript?

Answer 49

A Proxy is an object that acts as an intermediary between a target object and the code that interacts with it. It allows one to intercept and manipulate the behavior of an object.

Question 50

What is a Reflect API in JavaScript?

Answer 50

Reflect API is a built-in object that provides a way to interact with objects in a more reflective way. It allows us to perform the same operations as the usual Object methods, but it also has some additional methods and it throws exceptions when the methods fail.