No Dupe Else If - Denoland

Disallows using the same condition twice in an if/else if statement.

When you reuse a condition in an if/else if statement, the duplicate condition will never be reached (without unusual side-effects) meaning this is almost always a bug.

Invalid:

typescript

if (a) {}
else if (b) {}
else if (a) {} // duplicate of condition above

if (a === 5) {}
else if (a === 6) {}
else if (a === 5) {} // duplicate of condition above

Valid:

typescript

if (a) {}
else if (b) {}
else if (c) {}

if (a === 5) {}
else if (a === 6) {}
else if (a === 7) {}