
Interviews Questions - (Javascript)
Fundamentals
What is JavaScript?
- JavaScript is a high-level, interpreted programming language primarily used to add interactivity and dynamic behavior to
web pages.
- JavaScript is a high-level, interpreted programming language primarily used to add interactivity and dynamic behavior to
What are the core components of JavaScript?
- ECMAScript: The standardized specification for JavaScript.
- DOM (Document Object Model): Represents the structure and content of an HTML or XML document as a tree of objects.
- BOM (Browser Object Model): Represents the browser window and its components (e.g., history, location, navigator).
How do you include JavaScript in an HTML document?
- Inline: Within the
<script>
tag within the HTML. - External: Linking to a separate JavaScript file using the
<script src="..."></script>
tag.
- Inline: Within the
What are variables in JavaScript?
- Containers for storing data values. Declared using
let
,const
, orvar
.
- Containers for storing data values. Declared using
What are data types in JavaScript?
- Primitive: Number, String, Boolean, Null, Undefined, Symbol.
- Object: Complex data types like arrays, objects, functions.
Data Structures
What are arrays in JavaScript?
- Ordered collections of values.
How do you access elements in an array?
- Using array indices (e.g.,
array[0]
for the first element).
- Using array indices (e.g.,
What are objects in JavaScript?
- Collections of key-value pairs.
How do you access properties of an object?
- Using dot notation (e.g.,
object.property
) or bracket notation (e.g.,object['property']
).
- Using dot notation (e.g.,
Control Flow
What are conditional statements in JavaScript?
if
,else if
,else
.
What are loops in JavaScript?
for
,while
,do...while
,for...of
,for...in
.
What are functions in JavaScript?
- Reusable blocks of code that perform a specific task.
What are function arguments and parameters?
- Parameters are placeholders defined in the function declaration.
- Arguments are the actual values passed to the function when it's called.
Operators
What are the different types of operators in JavaScript?
- Arithmetic, comparison, logical, assignment, bitwise.
What is the difference between
==
and===
in JavaScript?==
performs type coercion (e.g., "1" == 1 is true).===
performs strict comparison (e.g., "1" === 1 is false).
DOM Manipulation
What is the Document Object Model (DOM)?
- Represents the structure of an HTML or XML document as a tree of objects.
How do you select HTML elements using JavaScript?
- Using methods like
getElementById()
,getElementsByClassName()
,querySelector()
, andquerySelectorAll()
.
- Using methods like
How do you change the content of an HTML element using JavaScript?
- Access the element's
innerHTML
ortextContent
property.
- Access the element's
How do you add, remove, or modify HTML elements using JavaScript?
- Using methods like
createElement()
,appendChild()
,removeChild()
,insertBefore()
.
- Using methods like
How do you handle events in JavaScript?
- Using event listeners (e.g.,
addEventListener()
).
- Using event listeners (e.g.,
Events
What are common JavaScript events?
click
,mouseover
,mouseout
,keydown
,keyup
,submit
,load
.
How do you prevent the default behavior of an event?
- Use
event.preventDefault()
.
- Use
JavaScript Objects
What is the
this
keyword in JavaScript?- Refers to the current object within a method.
What are constructors in JavaScript?
- Special methods used to create and initialize objects.
What are prototypes in JavaScript?
- Allow you to add properties and methods to objects after they are created.
Arrays
How do you add elements to an array in JavaScript?
- Using
push()
,unshift()
,splice()
.
- Using
How do you remove elements from an array in JavaScript?
- Using
pop()
,shift()
,splice()
.
- Using
How do you iterate over an array in JavaScript?
- Using
for
,for...of
,forEach()
.
- Using
Strings
- How do you manipulate strings in JavaScript?
- Using methods like
concat()
,slice()
,split()
,join()
,toUpperCase()
,toLowerCase()
.
- Using methods like
JSON
What is JSON?
- JavaScript Object Notation, a lightweight data-interchange format.
How do you parse JSON data in JavaScript?
- Using
JSON.parse()
.
- Using
How do you stringify JavaScript objects into JSON?
- Using
JSON.stringify()
.
- Using
Asynchronous JavaScript
What are callbacks in JavaScript?
- Functions that are passed as arguments to other functions and executed later.
What are promises in JavaScript?
- Represent the eventual completion (or failure) of an asynchronous operation and its resulting value.
- Represent the eventual completion (or failure) of an asynchronous operation and its resulting value.
What is async/await?
- A syntax for writing asynchronous code in a more synchronous-like manner.
Error Handling
- How do you handle errors in JavaScript?
- Using
try...catch...finally
blocks.
- Using
DOM Manipulation
How do you create a new HTML element using JavaScript?
document.createElement()
How do you add event listeners to HTML elements?
element.addEventListener('event', callback)
How do you modify the CSS styles of an element using JavaScript?
- Access the
style
property of the element.
- Access the
How do you get and set the value of an input field using JavaScript?
- Access the
value
property of the input element.
- Access the
JavaScript Libraries and Frameworks
What is jQuery?
- A popular JavaScript library that simplifies HTML traversal, event handling, and AJAX.
What is React?
- A JavaScript library for building user interfaces.
What is Angular?
- A full-featured JavaScript framework for building web applications.
What is Vue.js?
- A progressive framework for building user interfaces.
Advanced Topics
What are closures in JavaScript?
- Functions that have access to variables from the outer (enclosing) function's scope, even after the outer function has finished executing.
What is hoisting in JavaScript?
- The process of moving variable declarations to the top of their scope during compilation.
What is the difference between
let
,const
, andvar
?let
andconst
are block-scoped, whilevar
is function-scoped.let
allows reassignment, whileconst
does not.
What are arrow functions in JavaScript?
- A concise syntax for writing functions.
What is the
this
keyword in the context of arrow functions?this
refers to the surrounding object in arrow functions, not the object that the function is called on.
How can you improve the performance of your JavaScript code?
- Minimize DOM manipulation, use efficient algorithms, avoid unnecessary calculations, and optimize for garbage collection.
I hope these questions are helpful for your JavaScript interview preparation!
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