Understanding Control Structures in JavaScript

Control structures help you make decisions and control the flow of your program. They allow you to execute different parts of your code based on certain conditions. Here’s a look at the main control structures in JavaScript:

1. if

// Syntax:
if (condition) {
  // Code to execute if condition is true
}
 
// Example:
let age = 18;
if (age >= 18) {
  console.log("You are an adult.");
}
 

The if statement lets you run a block of code if a specific condition is true. It’s used for basic decision-making.

2. else if

// Syntax:
if (condition1) {
  // Code to execute if condition1 is true
} else if (condition2) {
  // Code to execute if condition2 is true
}
 
// Example:
let score = 85;
if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
}
 

The else if statement follows an if statement and lets you check multiple conditions. If the first if condition is false, else if allows you to check another condition.

3. else

// Syntax:
if (condition) {
  // Code to execute if condition is true
} else {
  // Code to execute if condition is false
}
 
// Example:
let temperature = 30;
if (temperature > 25) {
  console.log("It's hot outside.");
} else {
  console.log("It's cool outside.");
}
 

The else statement is used when none of the previous conditions are true. It allows you to execute a block of code as a fallback.

4. switch

// Syntax:
switch (expression) {
  case value1:
    // Code to execute if expression equals value1
    break;
  case value2:
    // Code to execute if expression equals value2
    break;
  default:
    // Code to execute if expression does not match any case
}
 
// Example:
let day = 2;
switch (day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  case 3:
    console.log("Wednesday");
    break;
  default:
    console.log("Invalid day");
}
 

The switch statement is used to handle multiple possible values for a single variable. It is an alternative to multiple if-else statements when you need to compare one value against many possible options.

5. case

// Syntax:
switch (expression) {
  case value1:
    // Code to execute
    break;
}
 
// Example:
let fruit = "Apple";
switch (fruit) {
  case "Apple":
    console.log("It's an apple.");
    break;
  case "Banana":
    console.log("It's a banana.");
    break;
}

The case keyword is used inside a switch statement to define a block of code that will run if the switch expression matches the case value.

6. default

// Syntax:
switch (expression) {
  default:
    // Code to execute if no case matches
}
 
// Example:
let color = "Red";
switch (color) {
  case "Blue":
    console.log("It's blue.");
    break;
  case "Green":
    console.log("It's green.");
    break;
  default:
    console.log("Unknown color");
}
 

The default keyword is used in a switch statement to define a block of code that will run if none of the case values match the switch expression. In this example, if color is neither "Blue" nor "Green", the message "Unknown color" will be printed.

Summary

• if: Executes code based on whether a condition is true.
• else if: Provides additional conditions to check if the initial if condition is false.
• else: Executes code when no previous conditions are true.
• switch: Handles multiple conditions by comparing one value to various possible values.
• case: Specifies a block of code to run if the switch expression matches a value.
• default: Specifies a block of code to run if none of the case values match.

These control structures allow you to manage the flow of your program and handle different scenarios effectively.