JavaScript Conditional Statements

• ★ Conditional statements are used to perform different actions based on different conditions.
• ★ Use if to specify a block of code to be executed, if a specified condition is true.
• ★ Use else to specify a block of code to be executed, if the same condition is false.
• ★ Use else if to specify a new condition to test, if the first condition is false.
• ★ Use switch to specify many alternative blocks of code to be executed

if statement

Syntax:

			if(condition){
					code to be executed if the condition is true
			}
		

Example

Note: Some special charaters can not be displayed if those charaters are used directly in your HTML file.

			& becomes &
 			< becomes &lt;
 			> becomes &gt;
 			" becomes &quot;
 			' becomes &#39;
		

			let a = 1;
			let b = 2;
			if(a < b){
					document.getElementById("p1").innerHTML = 'a < b';
			}
		

if...else statment

Syntax:

			if(condition){
					code to be executed if the condition is true
			}
			else{
					code to be executed if the condition is false
			}
		

Example

			let a = 1;
			let b = 2;
			if(a < b){
						document.getElementById("p1").innerHTML = 'a < b';
			}
			else{
						document.getElementById("p1").innerHTML = 'a >= b';
			}
		

if...else if...else statement

Syntax:

				if(condition1){
						code to be executed if the condition 1 is true
				}
				else if(condition 2){
						code to be executed if the condition 2 is true
				}
				else{
						code to be executed if the condition 2 is false
				}
		

Example

			let a = 1;
			let b = 2;
			if(a < b){
					document.getElementById("p1").innerHTML = 'a < b';
			}
			else if(a > b){
					document.getElementById("p1").innerHTML = 'a > b';
			}
			else{
					document.getElementById("p1").innerHTML = 'a==b';
			}
		

Switch statement

• ★ The switch statement is used to perform different actions based on different conditions.

			switch(expression){
			
			case x:
					code to be executed if expression == x
					break;
			
			case y:
					code to be executed if expression == y
					break;
	
			case z:
					code to be executed if expression == z
					break;
			
			default:
					code to be executed
			}
		

• ★ The switch expression is evaluated once;
• ★ The value of the expression is compared with the values of each case;
• ★ If there is a match, the associated block of code will be executed.
• ★ If there is no match, the default code block is executed.

			<p id="demo"></p>
			<script>
				let day;
				switch (new Date().getDay()) {
					case 0:
						day = "Sunday";
						break;

					case 1:
						day = "Monday";
						break;

					case 2:
						day = "Tuesday";
						break;

					case 3:
						day = "Wednesday";
						break;

					case 4:
						day = "Thursday";
						break;

					case 5:
						day = "Friday";
						break;

					case 6:
						day = "Saturday";
						break;
				}
				document.getElementById("demo").innerHTML = "Today is " + day;
			</script>
		

• ★ Example: https://www.w3schools.com/js/tryit.asp?filename=tryjs_switch

Can case Labels in switch Statements Be Any Data Type?

In JavaScript, the case labels in a switch statement must be values that can be strictly compared (===) to the expression inside switch().
Allowed Data Types for case Labels:

• 1. Using Numbers in case

				let num = 2;
				switch (num) {
				    case 1:
				        console.log("One");
				        break;
				    case 2:
				        console.log("Two");
				        break;
				    default:
				        console.log("Unknown number");
				}
			

• 2. Using Strings in case

				let fruit = "apple";
				switch (fruit) {
				    case "banana":
				        console.log("It's a banana.");
				        break;
				    case "apple":
				        console.log("It's an apple.");
				        break;
				    default:
				        console.log("Unknown fruit.");
				}
			

• 3. Using Boolean Values in case

				let isLoggedIn = true;
				switch (isLoggedIn) {
				    case true:
				        console.log("User is logged in.");
				        break;
				    case false:
				        console.log("User is logged out.");
				        break;
				}
			

• 4. Using Expressions in case

				let x = 10;
				switch (x % 2 === 0) { // This evaluates to true or false
				    case true:
				        console.log("Even number");
				        break;
				    case false:
				        console.log("Odd number");
				        break;
				}