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