JavaScript/lesson-05/variables.html at main · deep100x/JavaScript · GitHub

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<!-- in this lesson: -->
<!-- ------------------- -->
<!--

     Lesson 5 : Variables

     1. What is variable ?
     2. Variable name restriction
     3. Create a new variable using let
     4. Re-assigning a value to a variable
     5. 3 ways to create variable (let, const, var)
     6. typeof + variable

-->
<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="UTF-8" />
		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
		<title>Document</title>
	</head>
	<body>
		<script>
			//   🟨What is variable ?   --camelCase--

			//   Variable🟨 = 🟩Container
			//   🟩 <- we can save a value

			//   🟨Variable Name 🟥Restriction :-
			//   🟦1. Cant use special words. Example: let❌
			//        ❌ let let = 5;
			//        🟩 let let1 = 5;
			//   🟦2. Cant start a variable name with number
			//        ❌ let 1name = 3;
			//        🟩 let name1 = 5;
			//   🟦3. Cant use special characters except: $_
			//        🟩 let $name = 5;
			//        🟩 let _name = 5;

			//   🟨Create a new Variable using let
			let variable1 = 3
			console.log(variable1)

			const calculation = 2 + 2
			console.log(calculation)
			console.log(calculation + 2)

			const result = calculation + 2
			console.log(result)

			const message = "hello"
			console.log(message)
			console.log(";")

			//   🟨Re-assigning a value to a variable
			variable1 = 5
			console.log(variable1)

			//   🟨Syntax Rules for Re-assigning a value to a variable
			variable1 = 5
			console.log(variable1)

			//   🟨increase a value of a variable by a certain number
			variable1 = variable1 + 1
			console.log(variable1)

			//   🟨Naming Conventions
			//   🟦1. camelCase  : cartQuantity
			//   🟦2. PascalCase : CartQuantity
			//   🟦3. kebab-case : cart-quantity ❗(will not work in JavaScript)

			//   🟨3 ways to create variable
			//   🟦1. const variable2 = 3; (will not change in future)(Default)
			const variable2 = 20
			//   🟦2. var variable3 = 4; (has some issues)
			var variable3 = 30
			//   🟦3. let variable3 = 4; (will change in future)
			let variable4 = 40

			//   🟨typeof + variables
			console.log(typeof message)
			console.log(typeof variable2)

			//🟨Variable Swapping:

			let a = 5
			let b = 10

			// swap the values
			;[a, b] = [b, a]
			console.log("a : ", a)
			console.log("b : ", b)

			//🟨Increment and Decrement:

			let count = 5

			count++
			console.log("Incremented count : " + count)
			count--
			console.log("Incremented count : " + count)

			//🟨Calculate Area:

			const length = 10
			const width = 5
			const area = length * width
			console.log("Area of the rectangle : " + area)

			//🟨Concatenating Strings:

			var firstName = "Deep"
			var lastName = "Kothari"
			var fullName = firstName + lastName
			console.log("Full Name : ", fullName)

			//🟨Using Template Literals:

			var firstName = "Deep"
			var lastName = "Kothari"
			var fullName = `${firstName} ${lastName}`
			console.log(fullName)

			//🟨Convert String to Number:

			const numString = "42"
			const num = Number(numString)

			console.log("Original String : " + numString)
			console.log("As a number : " + num)
			console.log("Add 10 : " + (num + 10))

			//🟨Variable Scope:

			let globalVar = "I'am global"
			function localVarScope() {
				let localVar = "I'm local to the function"
				console.log(localVar)
			}

			localVarScope()
			console.log(globalVar)

			//🟨Check Variable Type:

			const value = true
			if (typeof value === "string") {
				console.log("It's a string")
			} else if (typeof value === "number") {
				console.log("It's a number")
			} else if (typeof value === "boolean") {
				console.log("It's a boolean")
			} else {
				console.log("It's something else")
			}

			//🟨Temperature Converter:

			var fahrenheit = 68
			var celsius = ((fahrenheit - 32) * 5) / 9
			console.log(`${fahrenheit}°F is ${celsius}°C`)

			//🟨Random Number Generator:

			var randomNumber = Math.floor(Math.random() * 10) + 1
			console.log("Random number : " + randomNumber)

			//🟨Age Calculator:

			const birthYear = 2003
			const currentYear = new Date().getFullYear()
			const age = currentYear - birthYear
			console.log(age)

			//🟨Variable Scope (Function vs. Block):

			if (true) {
				var varVariable = "I'm function-scoped"
				let letVariable = "I'm block-scoped"
				const constVariable = "I'm also block-scoped"
			}
			console.log(varVariable)
			console.log(letVariable)
			console.log(constVariable)

			//🟨Simple Calculator:

			const num1 = 10
			const num2 = 5
			const operator = "+"
			let result1
			switch (operator) {
				case "+":
					result1 = num1 + num2
					break
				case "-":
					result1 = num1 - num2
					break
				case "*":
					result1 = num1 * num2
					break
				case "/":
					result1 = num1 / num2
					break
				default:
					result1 = "Invalid operator"
			}
			console.log(`Result of ${num1} ${operator} ${num2} is ${result1}`)
		</script>
	</body>
</html>