switch (typeof something) isn't seen as exhaustive

🔎 Search Terms

• typeof
• switch
• narrow
• type guard

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about Type Guards

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.2#code/GYVwdgxgLglg9mABBAFgUwgawIIBtcA8AKgHwAUAznALZpQoxgDmAXIkQJRtGIDeAUIkQUA7jCipEZKAE8ADmjjBhNOg2Yc+gocgCGFNIgBEYENQBGaAE5GW2oRH2Gj5mE0ZRb9vQePm4cLhoumBeOj7OFDIWgWE6jr5G4AAmaMCMaMlxDk7GoJCwCNkRxnDmAFYYnnbhCZFQVoxMxUJWdCBWSFS09E0A3NoAvvyDQA

💻 Code

function checkAll<T>(something: T): T {
  switch (typeof something) {
    case "number":
    case "bigint":
    case "boolean":
    case "symbol":
    case "undefined":
    case "function":
    case "object":
    case "string":
      return something;
  }
}

🙁 Actual behavior

This emits the TS error: "Function lacks ending return statement and return type does not include 'undefined'.(2366)"

🙂 Expected behavior

No error, since all possible results of typeof are handled.

Additional information about the issue

It seems to only be an issue when the function argument is generic. It works if I switch the return type and parameter types to any, but I'm not sure that's a fair comparison.

Empieza ejecutando la reproducción proporcionada en TypeScript Playground y compara la función genérica con la versión any. Sigue cómo se gestionan el estrechamiento mediante typeof y la exhaustividad de switch para tipos genéricos; después, añade una prueba de regresión que muestre que todos los casos de typeof satisfacen el tipo de retorno sin TS2366.