The switch statement evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case. It provides a more readable alternative to a long series of if-else if statements when you have multiple, distinct values to check against a single variable.

Example 1: Basic Switch Statement

// Get the current day of the week as a number (0-6)
let day = new Date().getDay();
let dayName;

// Switch statement to find the name of the day
switch (day) {
  case 0:
    dayName = "Sunday";
    break;
  case 1:
    dayName = "Monday";
    break;
  case 2:
    dayName = "Tuesday";
    break;
  case 3:
    dayName = "Wednesday";
    break;
  case 4:
    dayName = "Thursday";
    break;
  case 5:
    dayName = "Friday";
    break;
  case 6:
    dayName = "Saturday";
}

console.log(`Today is ${dayName}.`);

Explanation: This code gets the current day of the week as a number. The switch statement then matches this number to a corresponding case and assigns the correct day name to the dayName variable.

Example 2: Switch with a Default Case

// Define a variable representing a user's subscription level
let userLevel = "gold";
let userPermissions;

// Switch statement to assign permissions based on subscription level
switch (userLevel) {
  case "admin":
    userPermissions = "Full Access";
    break;
  case "premium":
    userPermissions = "Access to premium content";
    break;
  case "member":
    userPermissions = "Access to member-only articles";
    break;
  default:
    userPermissions = "Guest Access"; // This runs if no other case matches
}

console.log(`Your permission level is: ${userPermissions}`);

Explanation: The default case in this switch statement acts as a catch-all. If the userLevel variable does not match any of the specified cases ('admin', 'premium', or 'member'), the default block is executed.

Example 3: Grouping Cases (Fall-through)

// Define a variable for a character grade
let grade = 'B';
let feedback;

// Switch statement to provide feedback based on the grade
switch (grade) {
  case 'A':
    feedback = "Excellent!";
    break;
  case 'B':
  case 'C':
    feedback = "Good job, you passed."; // Cases 'B' and 'C' share this feedback
    break;
  case 'D':
    feedback = "You can do better.";
    break;
  default:
    feedback = "You failed.";
}

console.log(feedback);

Explanation: This example demonstrates how to group multiple cases. Since there is no break statement after case 'B', the code "falls through" and executes the code for case 'C'.

Example 4: Importance of the 'break' Statement

// Define a variable for a product code
let productCode = 1;

// Switch statement to display product information
switch (productCode) {
  case 1:
    console.log("Product: Laptop");
    // Without 'break', it would continue to the next case
  case 2:
    console.log("Product: Keyboard");
    break; // Stops execution here
  case 3:
    console.log("Product: Mouse");
    break;
}

Explanation: If the break statement were omitted from case 1, the code would execute the console.log for "Product: Laptop" and then continue to execute the code for case 2, logging "Product: Keyboard" as well. The break keyword is essential for separating the logic of each case.

Example 5: Using Strings in Cases

// Define a variable for a browser name
let browser = "Chrome";
let compatibility;

// Switch statement to check browser compatibility
switch (browser) {
  case "Chrome":
  case "Firefox":
  case "Edge":
    compatibility = "Fully supported.";
    break;
  case "Safari":
    compatibility = "Partially supported.";
    break;
  default:
    compatibility = "Not supported.";
}

console.log(`Browser compatibility: ${compatibility}`);

Explanation: This demonstrates that case clauses are not limited to numbers. Here, we are using string values to check the name of a web browser and determine its compatibility level.

Example 6: Switch Inside a Function

// Function to get the name of a season based on the month number
function getSeason(month) {
  let season;
  // Switch statement to determine the season
  switch (month) {
    case 12:
    case 1:
    case 2:
      season = "Winter";
      break;
    case 3:
    case 4:
    case 5:
      season = "Spring";
      break;
    case 6:
    case 7:
    case 8:
      season = "Summer";
      break;
    case 9:
    case 10:
    case 11:
      season = "Autumn";
      break;
    default:
      season = "Invalid Month";
  }
  return season;
}

console.log(`The current season is ${getSeason(4)}.`); // Outputs: The current season is Spring.

Explanation: This example encapsulates a switch statement within a function. The function takes a month number as an argument and returns the corresponding season, making the logic reusable.

Example 7: Switch with Expressions in Cases

// Define a variable for a numeric value
let value = 15;
let result;

// Switch statement with boolean expressions in cases
switch (true) {
  case (value >= 0 && value <= 10):
    result = "Value is between 0 and 10";
    break;
  case (value > 10 && value <= 20):
    result = "Value is between 11 and 20";
    break;
  default:
    result = "Value is outside the defined ranges";
}

console.log(result);

Explanation: This less common but powerful pattern uses switch(true). Each case is an expression that evaluates to either true or false. The first case that evaluates to true is executed.