The comma operator (,) evaluates its operands, from left to right, and returns the second one. That's useful in some situations, but just wrong in a switch case. You may think you're compactly handling multiple values in the case, but only the last one in the comma-list will ever be handled. The rest will fall through to the default.

Similarly the logical OR operator (||) will not work in a switch case, only the first argument will be considered at execution time.

Noncompliant Code Example

switch a {
  case 1,2:  // Noncompliant; only 2 is ever handled by this case
    doTheThing(a);
  case 3 || 4: // Noncompliant; only '3' is handled
    doThatThing(a);
  case 5:
    doTheOtherThing(a);
  default:
    console.log("Neener, neener!");  // this happens when a==1 or a == 4
}

Compliant Solution

switch a {
  case 1:
  case 2:
    doTheThing(a);
  case 3:
  case 4:
    doThatThing(a);
  case 5:
    doTheOtherThing(a);
  default:
    console.log("Neener, neener!");
}