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swetha palani
swetha palani

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JavaScript in 1 Day – Quick Beginner Guide

What is JavaScript?

JavaScript is the programming language of the Web. It makes web pages interactive and dynamic by:

  • Updating and changing both HTML and CSS.
  • Calculating, manipulating, and validating data.
  • Calculating, manipulating, and validating data.

Responding to user events like clicks, scrolls, and inputs.

JavaScript Syntax Basics

JavaScript syntax defines rules for how programs are constructed.
Variable Declaration:

var x;
let y;

x = 5;
y = 6;
let z = x + y;
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JavaScript Values

JavaScript syntax defines two types of values:

Fixed values → called Literals
Example: 5, "Hello", true

Variable values → stored in Variables
Example: let name = "Swetha"
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JavaScript Comments

Comments are used to explain code and prevent it from running.
➤ Single-Line Comment:

// This is a comment
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➤ Multi-Line Comment:
/* This is a

   multi-line comment */
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JavaScript Variables

Variables are containers for storing data.

You can declare variables in 4 ways:

Automatically (not recommended)

Using **var** – old way

Using **let** – modern, block-scoped

Using **const** – block-scoped & constant
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let in JavaScript

Key Features of let:

  • Block Scope
  • Must be declared before use
  • Cannot be redeclared in the same scope 
{
  let x = 2;
}
// x is not accessible here – it’s block scoped
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const in JavaScript

The const keyword is also introduced in ES6 (2015).
** Key Features of const:**

  • Block Scope
  • Cannot be Redeclared
  • Cannot be Reassigned 
const pi = 3.14;
pi = 3.14159; // ❌ Error: Assignment to constant variable
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Use const for variables that should never change.

JavaScript is a powerful tool for web development. In just one day, you can:

  • Learn how to declare variables
  • Understand data types
  • Add comments to explain your code
  • Use let and const effectively

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