Why Does NestJS Include success and message in Responses?

📌 Why Does NestJS Include `success` and `message` in Responses?

In NestJS, developers often explicitly include success and message fields in their responses, while in Java (Spring Boot), we rely on HTTP status codes (ResponseEntity) for this purpose.

1️⃣ Key Differences: NestJS vs. Spring Boot

Feature	NestJS (JavaScript/TypeScript)	Spring Boot (Java)
How Responses Work?	Explicitly constructs API responses with `success`, `message`, and `data`.	Uses `ResponseEntity<T>` with HTTP status codes.
How Errors Work?	Errors are usually wrapped inside the same JSON response structure.	Uses `ExceptionHandler` or `ResponseEntityExceptionHandler` with HTTP error codes.
Default Pagination Response?	Custom DTOs often include `success` and `message`.	`Page<T>` from Spring Data does not include `success` and `message`.

2️⃣ Why NestJS Includes `success` and `message` by Default?

In Java (Spring Boot), we typically rely on HTTP status codes (like 200 OK, 400 Bad Request, 500 Internal Server Error) to indicate success or failure.

But in NestJS, it's more common to explicitly return structured responses like:

json
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{
  "success": true,
  "message": "Users fetched successfully",
  "data": {
    "items": [...],
    "totalPages": 5,
    "count": 50
  }
}

✔ This ensures every response follows a consistent format, even in case of errors.

✔ Helps frontend developers always know what to expect (success, message, data).

3️⃣ Why Java Uses `ResponseEntity<T>` Instead

In Spring Boot, we typically return responses directly using ResponseEntity<T> and rely on HTTP status codes for indicating success or failure.

Example in Java:

java
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@GetMapping("/users")
public ResponseEntity<Page<UserDTO>> getUsers(Pageable pageable) {
    Page<UserDTO> users = userService.getUsers(pageable);
    return ResponseEntity.ok(users);
}

The HTTP status (200 OK) already indicates success.

If there’s an error, we throw an exception like:

java
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throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Invalid request");

Spring will automatically return:

json
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{
  "timestamp": "2024-03-08T12:00:00Z",
  "status": 400,
  "error": "Bad Request",
  "message": "Invalid request",
  "path": "/users"
}