JavaScript Fundamentals / Control Flow

Conditional Statements

🧈 Conditional Statement

Very often when you write code, you want to perform different actions for different decisions.

You can use conditional statements in your code to do this.

In JavaScript we have the following conditional statements:

  • 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

🔰 The if Statement

Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

Syntax :

if (*condition*) {  
//  *block of code to be executed if the condition is true*
}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate a JavaScript error. Example :

Make a "Good day" greeting if the hour is less than 18:00:

let hour = 15; 
let greeting;
if (hour < 18) {
  greeting = "Good day";
}
console.log(greeting);
Good day

🧩 The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax :

if (*condition*) {  
   //  *block of code to be executed if the condition is true*
} else {  
  //  *block of code to be executed if the condition is false*
}

Example :

If the hour is less than 18, create a "Good day" greeting, otherwise "Good evening" :

let time = 21; 
let greeting;

if (time < 20) {
  greeting = "Good morning";
} else {
  greeting = "Good evening";
}

console.log(greeting);
Good evening

💠The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax :

if (*condition1*) {  
    //  *block of code to be executed if condition1 is true*
} else if (*condition2*) {  
   //  *block of code to be executed if the condition1 is false and condition2 is true*
} else {  
  //  *block of code to be executed if the condition1 is false and condition2 is false*
}

Example :

let time = 14; 
let greeting;

if (time < 10) {
   greeting = "Good morning";
} else if (time < 20) {
   greeting = "Good day";
} else {
   greeting = "Good evening";
}

console.log(greeting);
Good day

🔄 The Switch Statement

The switch statement is used to perform different actions based on different conditions, just like a board switch in real life:

🧠 "If I press button 1, turn on light. If I press button 2, turn on fan..."

It's an alternative to multiple if...else if conditions — and is easier to read when you have many options.

This is how it works:

  • 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 is executed.

  • If there is no match, the default code block is executed.

Syntax :

switch(*expression*) {  
   case *x*:    
       *// code block*    
       break;  
   case *y*:    
       *// code block*    
       break;  
   default:    
      // *code block*
   }

Example :

let day = 2;
let message;

switch(day) {
   case 1:
     message = "Monday";
     break;
   case 2:
     message = "Tuesday";
     break;
   case 3:
     message = "Wednesday";
     break;
   default:
      message = "Another day";
}

console.log(message);
Tuesday

📌 Key Notes:

  • break stops the execution after the match — very important!

  • default runs if no case matches

  • switch works best when comparing a single value against many fixed values