UNIT 3: JAVASCRIPT

JavaScript is a widely used programming language that is mainly used for client-side scripting in web development. In this unit, we will go through the fundamentals of JavaScript, including client-side scripting, basic JavaScript concepts, variables, functions, conditions, and loops.

3.1. Client-Side Scripting

Client-side scripting refers to the code that runs on the user's browser rather than on the web server. When a user interacts with a webpage, client-side scripts are executed to make the web page dynamic and interactive without needing to refresh or make a request to the server.

Characteristics:

It runs on the user's device (browser).
It doesn't need a server to interact with the client (though it can interact with the server via APIs).
It improves the user experience by reducing load times and enabling interactive features like form validation, animations, etc.

Example:

When you fill out a form, client-side scripting can validate if the fields are filled correctly before sending the data to the server.

Client-Side Flowchart:

[User Input] --> [Browser] --> [Client-Side Script (JavaScript)] --> [Updated Webpage]

3.2. What is JavaScript?

JavaScript is a high-level, interpreted programming language used primarily for creating interactive effects within web browsers. It allows developers to add functionality to web pages by interacting with HTML and CSS.

Key Points:

JavaScript is dynamic, meaning it can change the content and appearance of a webpage in real time.
It is a scripting language, which means it is typically used to automate tasks, manipulate web page elements, and manage asynchronous events.
JavaScript can interact with HTML and CSS to create dynamic and interactive websites.

Usage:

Form validation.
Animation and graphics (e.g., using libraries like Canvas).
Event handling (e.g., mouse clicks, key presses).
Data manipulation (e.g., working with arrays, objects).

3.3. Simple JavaScript

In simple JavaScript, we typically write statements to define variables, functions, and other logic to manipulate data or interact with HTML elements.

Example:

// Simple JavaScript example
let greeting = "Hello, World!";  // Defining a variable
console.log(greeting);  // Output to the console

In the above code:

let is used to declare a variable.
console.log() prints the value of the variable to the browser’s console.

Key Concepts:

Variables store values.
Functions are used to group code for reuse.
Events can be used to trigger actions, like clicking a button.

3.4. Variables

Variables are used to store data that can be used later in the code. JavaScript provides several ways to declare variables using the keywords var, let, and const.

var: The older way of declaring variables.
let: A modern approach to declare variables that are block-scoped.
const: Used for values that should not change after initialization (constant values).

Example:

let name = "John"; // Variable declaration using let
const age = 30;    // Constant declaration

Types of Variables:

String: Represents text, e.g., "Hello"
Number: Represents numeric values, e.g., 100
Boolean: Represents true/false values, e.g., true
Array: Used to store a collection of values, e.g., [1, 2, 3]
Object: Used to store key-value pairs, e.g., { name: "John", age: 30 }

Flowchart for Variable Declaration:

[Declare Variable] --> [Store Data] --> [Use Data in Code]

3.5. Functions and Conditions

Functions

A function is a block of reusable code that can be called with a specific name to perform a task.

Syntax of Function:

function greet(name) {
  console.log("Hello, " + name);
}

greet("Alice");  // Output: Hello, Alice

Key Concepts:

Function Declaration: Defines a function.
Function Call: Executes the function.
Parameters: The values passed into the function.
Return: Functions can return a value.

Flowchart for Function:

[Define Function] --> [Call Function] --> [Perform Task]

Conditions

Conditional statements allow the program to make decisions based on certain conditions. The most common conditional statements are if, else, and else if.

Example:

let age = 20;

if (age >= 18) {
  console.log("You are an adult.");
} else {
  console.log("You are a minor.");
}

Flowchart for Conditions:

[Condition (e.g., age >= 18)] 
     |
   Yes -> [Execute Task]  
     |
   No -> [Execute Alternate Task]

In this example:

If age is greater than or equal to 18, it prints "You are an adult."
Otherwise, it prints "You are a minor."

3.6. Loops and Repetition

Loops are used to repeat a block of code multiple times until a specific condition is met. The most common types of loops are for, while, and do-while.

For Loop

The for loop is used when the number of iterations is known in advance.

Example:

for (let i = 0; i < 5; i++) {
  console.log(i);
}

Flowchart for For Loop:

[Initialize Counter] --> [Condition Check] --> [Execute Task] --> [Update Counter]
        ↑                                 ↓
      (End if False) <--------------------|

In the above example:

The loop starts with i = 0.
The loop runs as long as i is less than 5.
After each iteration, i is incremented by 1.

While Loop

The while loop runs as long as the condition is true.

Example:

let i = 0;
while (i < 5) {
  console.log(i);
  i++;
}

Flowchart for While Loop:

[Condition Check] --> [Execute Task] --> [Update Counter] --> [Condition Check]
        ↑                                 ↓
      (End if False) <--------------------|

Do-While Loop

The do-while loop ensures that the code block is executed at least once, even if the condition is initially false.

Example:

let i = 0;
do {
  console.log(i);
  i++;
} while (i < 5);

Summary

In this unit, we covered the following key JavaScript concepts:

Client-Side Scripting: JavaScript runs in the browser to make web pages interactive and dynamic.
What is JavaScript?: JavaScript is a language used for scripting interactive elements on websites.
Simple JavaScript: A basic understanding of how to write and execute JavaScript code.
Variables: JavaScript stores data in variables, which can be manipulated throughout the program.
Functions and Conditions: Functions group code into reusable blocks, and conditions allow decisions to be made based on specific criteria.
Loops and Repetition: Loops enable repeating actions, saving time and making code more efficient.

JavaScript is a powerful tool for creating dynamic web applications.

UNIT 3: JAVASCRIPT