Switch

A switch is a conditional statement that performs actions based on different conditions. It uses strict ( === ) comparison to match the conditions and executes the code blocks of matched condition. The syntax of the switch expression is shown below.

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

The expression is evaluated once and is compared with each case. If a match is found, then the associated code block is executed if not default code block is executed. The break keyword stops the execution and can be placed anywhere. In its absence, the next condition is evaluated even if the conditions are not matched.

An example of getting a weekday name based on the switch condition is shown below.

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";
}

In multiple matching cases, the first matching value is selected, if not the default value is selected. In the absence of default and no matching case, the program continues to the next statement(s) after switch conditions.

let dayOfWeek = "Monday";
let result;
// check if it's a weekday or the weekend
switch (dayOfWeek) {
  case "Monday":
  case "Tuesday":
  case "Wednesday":
  case "Thursday":
  case "Friday":
    result = "It's a weekday";
    break;
  case "Saturday":
  case "Sunday":
    result = "It's the weekend";
    break;
  default:
    result = "Invalid day of the week";
    break;
}

assert(result == "It's a weekday" );