javascript - Switch case with conditions

Question

Am I writing the correct switch case with conditions?

var cnt = $("#div1 p").length;
alert(cnt);

switch (cnt) {
  case (cnt >= 10 && cnt <= 20):
    alert('10');
    break;
  case (cnt >= 21 && cnt <= 30):
    alert('21');
    break;
  case (cnt >= 31 && cnt <= 40):
    alert('31');
    break;
  default:
    alert('>41');
}

For some reason, the alert does not occur when the conditions are matched!

Answer 1

A switch works by comparing what is in switch() to every case.

switch (cnt) {
    case 1: ....
    case 2: ....
    case 3: ....
}

works like:

if (cnt === 1) ...
if (cnt === 2) ...
if (cnt === 3) ...

Therefore, you can't have any logic in the case statements.

switch (cnt) {
    case (cnt >= 10 && cnt <= 20): ...
}

works like

if (cnt === (cnt >= 10 && cnt <= 20)) ...

and that's just nonsense. :)

Use if () { } else if () { } else { } instead.