Front-End Interview Questions Basic

1.Java and JavaScript

java

• A programming language used to build applications like Android apps, enterprise software, banking systems, etc.

• Runs on JVM (Java Virtual Machine)

• Strict, strongly typed (you must specify data types)

javaScript

• A scripting language mainly used to make websites interactive (front-end & back-end).

• Runs in web browsers and also on servers using Node.js

• Loose, dynamically typed (no need to specify data types)

1. *Function and Arrow Function *

Function

• A function is a block of code defined using the function keyword that can be called anytime to perform a task

• It has its own this, arguments, and is hoisted.

Example:

function add(a, b) {
  return a + b;
}

Arrow Function

• An arrow function is a shorter and modern way to write functions using the => arrow syntax

• It does not have its own this or arguments, and it is not hoisted.

Example:

const add = (a, b) => a + b;

3.var let const

var

• var is the old way of declaring variables in JavaScript. It is function-scoped, can be redeclared, and can be updated.

var x = 10;
x = 20;

var x = 30;

• Old variable declaration

• Function scope

• Re-declare > Yes

• Update value > Yes

• Use Case > Older code, not recommended

let

• let is the modern variable declaration. It is block-scoped, cannot be redeclared in the same block, but can be updated.

let y = 10;
y = 20;

let y = 30;

• Modern variable declaration

• Block scope

• Re-declare > no

• Update value > Yes

• Use Case > Normal variables

const

• const is used to declare constants. It is block-scoped, cannot be updated, cannot be redeclared

const z = 10;
z = 20;

• Constant variable declaration

• Block scope

• Re-declare > no

• Update value > no

• Constant values

4.HTML and CSS

HTML

• HTML (HyperText Markup Language) HTML is used to create the structure of a webpage. It decides what content appears on the page

** Example:**

• Headings
• Paragraphs
• Images
• Buttons
• Forms

<h1>Hello World</h1>
<p>This is a paragraph.</p>

CSS

-CSS (Cascading Style Sheets)

• CSS is used to style the webpage.

• It decides how the content looks.

Example:

• Colors
• Fonts
• Layout
• Height & width
• Backgrounds

h1 {
  color: blue;
  font-size: 30px;
}

5.ID and Class Selector

ID

• An ID is a unique name given to a single HTML element

• Used when you want to style only one specific element.

• Symbol in CSS (#)

• Special elements (header, footer, section)

HTML

<div id="header">Home</div>

**CSS**
#header {
  color: blue;
}

Class

• A class is used to style multiple elements with the same design.

• Used when you want to apply the same style to more than one element

• Symbol in CSS (.)

• Repeated styling (buttons, titles, cards)

HTML

<div class="header">Home</div>

**CSS**
.header {
  color: blue;
}