try / catch / finally

finally runs always

finally runs whether or not the try threw — even if the catch threw, even if a return happened. It's the only safe place for cleanup that MUST happen.

function withConnection(work) {
  const conn = openConnection();
  try {
    return work(conn);
  } catch (err) {
    console.error("work failed:", err);
    throw err;
  } finally {
    conn.close();   // ALWAYS runs
  }
}

Common shape

The "wrap a risky thing, always tear it down" pattern:

• Open a file → finally close it.
• Start a transaction → finally rollback if not committed.
• Show a spinner → finally hide it.

Re-throwing

throw err inside a catch re-throws the same error. The finally still runs first; then the throw propagates to the caller. The original stack is preserved.

return inside finally is a trap

return inside finally overrides any return from try/catch and silently swallows pending throws. Always use finally for SIDE EFFECTS, never for return values.