Error Handling

1// Custom error classes
2class ApiError extends Error {
3  constructor(
4    message: string,
5    public statusCode: number,
6    public endpoint: string
7  ) {
8    super(message);
9    this.name = "ApiError";
10  }
11}
12 
13class ValidationError extends Error {
14  constructor(
15    message: string,
16    public field: string
17  ) {
18    super(message);
19    this.name = "ValidationError";
20  }
21}
22 
23// Result type pattern (like Rust's Result)
24type Result<T, E = Error> =
25  | { success: true; data: T }
26  | { success: false; error: E };
27 
28async function fetchWithResult<T>(url: string): Promise<Result<T>> {
29  try {
30    // Simulated fetch
31    await new Promise((resolve) => setTimeout(resolve, 100));
32    const data = { message: "Success" } as T;
33    return { success: true, data };
34  } catch (error) {
35    return {
36      success: false,
37      error: error instanceof Error ? error : new Error(String(error))
38    };
39  }
40}
41 
42// Using the Result pattern
43async function processData(): Promise<void> {
44  const result = await fetchWithResult<{ message: string }>("/api/data");
45 
46  if (result.success) {
47    console.log("Data:", result.data.message);
48  } else {
49    console.error("Failed:", result.error.message);
50  }
51}
52 
53// Error type narrowing
54async function handleRequest(): Promise<void> {
55  try {
56    throw new ApiError("Not found", 404, "/users/123");
57  } catch (error) {
58    if (error instanceof ApiError) {
59      console.log(`API Error [${error.statusCode}]: ${error.message}`);
60      console.log(`Endpoint: ${error.endpoint}`);
61    } else if (error instanceof ValidationError) {
62      console.log(`Validation Error on ${error.field}: ${error.message}`);
63    } else if (error instanceof Error) {
64      console.log(`Unknown error: ${error.message}`);
65    } else {
66      console.log("Something went wrong");
67    }
68  }
69}
70 
71// Run examples
72processData();
73handleRequest();