Error response

Since the error response is also transferred using JSON format between the server and the client, it must be transformed again on the client into a class representing the PTSQ error response. When using clients working with Tanstack query, the error response type is automatically set to PtsqClientError. Because Tanstack query does not use Promise objects to return results from the server, there is no need to further redefine the error response type.

However, by using a traditional client that returns the response in a Promise object, the error response must be rewritten because neither Promise nor the async/await constructs support defining error types. The rewriting occurs when the exception itself is checked. TypeScript allows you to define a predicate for a function that returns a boolean. The predicate is the type of function parameter that is set if the function returns true.

// async/await
try {
  const response = await client.user.list.query(...);
} catch(error) {
  if(PtsqClientError.isPtsqClientError(error)) {
    console.error(error.code);
  }
}
 
// Promise
client.user.list.query(...).then(...).catch((error) => {
  if(PtsqClientError.isPtsqClientError(error)) {
    console.error(error.code);
  }
});

Inside the PtsqClientError.isPtsqClientError(error) condition, the exception type is mapped from the unknown type to the PtsqClientError type and thus it is possible to safely access the PTSQ properties of the error response.