JSP 1 : Variables, Data Types, Operators

Introduction JavaScript (JS) is a high-level, interpreted programming language mostly used as a client-side scripting language It allows Developers to create interactive and dynamic webpages by manipulating the Document Object Model (DOM) which we shall discuss later. VARIABLES A variable is a container in which we can store values/data. Terms: 1. Variable declaration This is the process of defining a new variable using a keyword (var, let, or const) 2. Variable Initialization This is the process of assigning an initial value to a variable after it has been declared 3. Variable assignment Is the act of giving a variable a specific value 4. Variable look up expression The process of accessing a value of a variable by its name within the code (eg: using a console.log to print the value of the variable within the console) let greeting = "Hello, World!"; console.log(greeting); Hello, World! KEY WORDS 1. var (Old Way of Declaring Variables) ✅ Can be changed (reassigned) ✅ Can be declared again (redeclared) ❌ Works in function scope (not block scope) ❌ Has hoisting issues (explained below) NOTE WE'LL COVER SCOPE & HOISTING BETTER LATER ON var name = "Alice"; var name = "Bob"; // ✅ No error (but can be confusing) console.log(name); // Output: Bob Hoisting issues: console.log(x); // Output: undefined (NOT an error but still confusing!) var x = 10; 2. let (The Better Way) ✅ Can be changed (reassigned) ✅ Works in block scope (inside {}) ✅ Fixes the hoisting issue ❌ Cannot be declared again in the same scope let age = 25; age = 30; // ✅ Allowed (Reassignment) console.log(age); // Output: 30 let city = "Nairobi" let city = "Mombasa" // ❌ ERROR: Cannot redeclare 'city' 3. const (The Best Choice for Fixed Values) ✅ Cannot be changed (reassigned) ✅ Cannot be declared again ✅ Works in block scope ❌ Must be initialized when declared const PI = 3.1415 PI = 3.14 // ❌ ERROR: Cannot reassign a 'const' variable console.log(PI); // Output: 3.1415 TABULAR SUMMARY

Feb 25, 2025 - 14:00

JSP 1 : Variables, Data Types, Operators

Introduction
JavaScript (JS) is a high-level, interpreted programming language mostly used as a client-side scripting language

It allows Developers to create interactive and dynamic webpages by manipulating the Document Object Model (DOM)
which we shall discuss later.

VARIABLES

A variable is a container in which we can store values/data.

Terms:

1. Variable declaration
This is the process of defining a new variable using a keyword (var, let, or const)

2. Variable Initialization

This is the process of assigning an initial value to a variable after it has been declared

3. Variable assignment

Is the act of giving a variable a specific value

4. Variable look up expression
The process of accessing a value of a variable by its name within the code
(eg: using a console.log to print the value of the variable within the console)


let greeting = "Hello, World!";
console.log(greeting); 

Hello, World!

KEY WORDS

1. var (Old Way of Declaring Variables)
✅ Can be changed (reassigned)
✅ Can be declared again (redeclared)
❌ Works in function scope (not block scope)
❌ Has hoisting issues (explained below)

NOTE WE'LL COVER SCOPE & HOISTING BETTER LATER ON

var name = "Alice";
var name = "Bob"; // ✅ No error (but can be confusing)
console.log(name); // Output: Bob

Hoisting issues:

console.log(x); // Output: undefined (NOT an error but still 
                                                  confusing!)
var x = 10;

2. let (The Better Way)

✅ Can be changed (reassigned)
✅ Works in block scope (inside {})
✅ Fixes the hoisting issue
❌ Cannot be declared again in the same scope

let age = 25;
age = 30;  // ✅ Allowed (Reassignment)
console.log(age); // Output: 30
let city = "Nairobi"
let city = "Mombasa" // ❌ ERROR: Cannot redeclare 'city'

3. const (The Best Choice for Fixed Values)
✅ Cannot be changed (reassigned)
✅ Cannot be declared again
✅ Works in block scope
❌ Must be initialized when declared


const PI = 3.1415
PI = 3.14 // ❌ ERROR: Cannot reassign a 'const' variable
console.log(PI); // Output: 3.1415

TABULAR SUMMARY