JavaScript switch

switch (fruit) {
  case "apple":
    console.log("Crunchy!");
    break;
  case "banana":
    console.log("Potassium!");
    break;
  default:
    console.log("A mystery fruit.");
}

1. The value in brackets is compared with each case using strict equality (===).
2. When a case matches, its code runs.
3. break ends the switch. Without it, the code falls through into the next case and runs that too.
4. default runs if nothing matched, much like a final else.

Because the comparison is strict, case 1 won't match the string "1". Values read from forms or the page are strings, so convert them first if your cases are numbers.

Stack cases with no code between them to share one block:

case "Saturday":
case "Sunday":
  console.log("Weekend!");
  break;

This is the one situation where falling through is useful and deliberate. Anywhere else, a missing break is almost always a bug.

switch uses strict equality (===) to compare the value with each case. That means switch (input) with case 1: won't match when input is the string "1", which is a common surprise when values come from form fields or URLs. Convert first with Number(input), or write the cases as strings.

Each case only marks a starting point. Once a case matches, JavaScript runs every line below it, through later cases too, until it reaches a break or return. Leaving out break by mistake is the classic switch bug, but doing it on purpose is how several cases share the same code. Inside a function, return ends the switch and the function at once, so you don't need break after it.

In a function, return can replace break, because returning ends the function straight away:

function dayType(day) {
  switch (day) {
    case "Saturday":
    case "Sunday":
      return "weekend";
    default:
      return "weekday";
  }
}

This pattern is compact and avoids forgotten break statements entirely.