no-dupe-else-if

In an if ... else if chain, a branch only runs if every condition before it was false. If a condition repeats an earlier one, its branch can never run. It's usually a copied line where someone forgot to change the condition.

The rule also understands || and &&. After if (a || b), both else if (a) and else if (b && c) are dead. The order of the operands doesn't matter.

This rule is on by default.

Configure

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

[lint.rules]
"no-dupe-else-if" = "off" # or "warn"

Examples

Reported:

if (status === "active") {
  enable();
} else if (status === "paused") {
  pause();
} else if (status === "active") {
  archive();
}

Not reported:

if (status === "active") {
  enable();
} else if (status === "paused") {
  pause();
} else if (status === "archived") {
  archive();
}

A condition that's narrower than an earlier one is reported too:

if (user.isAdmin || user.isOwner) {
  showAll();
} else if (user.isOwner && user.isVerified) {
  showMost();
} else if (user.isAdmin) {
  showSome();
}

Put the narrower condition first:

if (user.isOwner && user.isVerified) {
  showMost();
} else if (user.isAdmin || user.isOwner) {
  showAll();
}