no-duplicate-case

A switch runs the first case that matches. A second case with the same test is never chosen, so its code only runs if the case above it falls through. It's usually a copied case where someone forgot to change the label.

Two labels are the same if their source text is the same, ignoring whitespace and comments.

This rule is on by default.

Configure

On by default as an error. To turn it off:

[lint.rules]
"no-duplicate-case" = "off" # or "warn"

Examples

Reported:

switch (event.key) {
  case "ArrowUp":
    moveUp();
    break;
  case "ArrowDown":
    moveDown();
    break;
  case "ArrowUp":
    selectPrevious();
    break;
}

Not reported:

switch (event.key) {
  case "ArrowUp":
    moveUp();
    break;
  case "ArrowDown":
    moveDown();
    break;
  case "PageUp":
    selectPrevious();
    break;
}

Labels don't have to be literals:

switch (true) {
  case size > limit:
    reject();
    break;
  case size > limit:
    warn();
    break;
}