Avoid throw function

avoid-throw-function.ts

// Suppose we have following code:

class APIError extends Error {}

function throwAPIError(message: string) {
  // complicated logic...

  throw new APIError(message);
}

export async function handleLogin(body: { username: string; encryptedPassword }): Promise<User> {
  const result = validate(body);
  if (!result.success) {
    // This sucks
    throwAPIError("invalid data");
  }
  
  return fetchUser(result.data.username);
}



// When we saw the `handleLogin`, we can't know the code stops in `throwAPIError`
// without looking at the function's implementation detail.
//
// Thus I prefer like this.

export async function handleLogin(body: { username: string; encryptedPassword }): Promise<User> {
  const result = validate(body);
  if (!result.success) {
    return throwAPIError("invalid data");
  }
  
  return fetchUser(result.data.username);
}



// But the above code is still insufficient for me.
// We can improve it like this:

function buildAPIError(message: string): APIError {
  // complicated logic...

  return new APIError(message);
}
  
export async function handleLogin(body: { username: string; encryptedPassword }): Promise<User> {
  const result = validate(body);
  if (!result.success) {
    throw buildAPIError("invalid data");
  }
  
  return fetchUser(result.data.username);
}



// I believe the last code is much more understandable though this may be a personal preference.