01.Variables and Datatypes

Data Types in JavaScript

JavaScript supports several types of data that variables can store. Here are the main ones, along with examples:

1. Numbers

Numbers in JavaScript can be either integers or floating-point values. JavaScript treats both as the same type, so there is no separate int or float.
let count = 10; // Integer let temperature = 98.6; // Floating-point number

2. String

Strings represent textual data, enclosed either in single (') or double (") quotes.

Example:
let greeting = "Hello, World!"; // String variable

3. Boolean

Boolean values can only be either true or false, used primarily for conditional statements.

Example:
let isJavaScriptFun = true; // Boolean variable

4. Undefined

A variable is undefined if it has been declared but not assigned a value.

Example:
let result; // Undefined variable console.log(result); // Output: undefined

5. Null

The null type represents the intentional absence of any object value. It is often used when we want to explicitly clear a variable.

Example:
let user = null; // Null variable

6. Object Literals

Objects in JavaScript are a collection of properties, where each property is defined by a key-value pair. An object can hold various data types.

Example:
const person = { firstName: "John", lastName: "Doe", age: 30, isMarried: true }; // Object literal
Note:
"null" simply means the value of nothing, while "undefined" refers to the absence of value

If you want to build something(Website), the first thing that you do is reserve memory and we have various ways to do this in JavaScript
var, let, and const

1. var Declaration
The var keyword is one of the oldest ways to declare variables in JavaScript. Variables declared using var are function-scoped and can be redeclared or updated.
var name = "John"; // Declaring and initializing a string variable name = "Doe"; // Reassigning a new value

2. let Declaration

Introduced in ES6, let is block-scoped, meaning the variable only exists within the surrounding block or curly braces {}. It cannot be redeclared in the same scope, though it can be updated.
let age = 25; // Declaring a number variable age = 30; // Reassigning a new value

3. const Declaration

The const keyword is used to declare a constant variable, which cannot be reassigned after its initial value. Like let, it is block-scoped.
const birthYear = 1995; // Declaring a constant // birthYear = 2000; // This will throw an error, as constants can't be reassigned

The Difference Between var, let, and const

• Scope:

  • var is function-scoped.

  • let and const are block-scoped.

• Redeclaration:

  • var can be redeclared and updated.

  • let can be updated but not redeclared in the same scope.

  • const can neither be redeclared nor updated.

• Hoisting:

  • var is hoisted, meaning it is accessible before its declaration, albeit with an undefined value.

  • let and const are also hoisted but are not initialized, so accessing them before declaration results in a ReferenceError.