Common Scenarios

Malformed JSON Handling

If a client sends invalid JSON (e.g., missing brackets or trailing commas), standard Express apps might crash or expose stack traces.ds-express-errors automatically catches SyntaxError from body-parser and returns a clean 400 Bad Request.

Request (Invalid JSON):

POST /users
{ "name": "Alice", }  <-- Trailing comma error

Important

url, stack, method are available in development mode, if you want to change that setting, you can redefine them by setConfig

Response:

{
    "status": "error", 
    "method": "POST",
    "url": "/users",
    "message": "Unexpected token } ... is not valid JSON",
    "stack": ...
}

Handling Duplicate Database Entries

When using MongoDB (Mongoose) or Prisma, unique constraint violations (e.g., registering with an existing email) often crash the app or return 500 errors. The library automatically detects these codes (like Mongo's 11000) and converts them to 400 Bad Request.

Controller Code:

javascript

module Copy

import { asyncHandler } from 'ds-express-errors';
    // No try-catch needed!
const registerUser = asyncHandler(async (req, res) => {
    // If email exists, DB throws error -> Library catches it -> Returns 400
    const user = await User.create(req.body); 
    res.status(201).json(user);
});

Response:

{
    "status": "fail",
    "method": "POST", 
    "url": "/users",
    "message": "Duplicate field value entered: {email:test@example.com}",
    "stack": ...
}

External Service Failures

When your API acts as a gateway to other services (e.g., Stripe, AWS, or microservices), failures in downstream services should be reported correctly.

Use BadGateway (502) when the upstream service returns an invalid response.

Use ServiceUnavailable (503) when the upstream service is down.

javascript

module Copy

import { Errors } from 'ds-express-errors';

const processPayment = asyncHandler(async (req, res) => {
    try {
        await stripe.charges.create({...});
    } catch (err) {
        // Wrap the external error
        throw Errors.BadGateway('Payment provider is not responding');
    }
});

Unsupported Libraries

Handling Unsupported Libraries: Using a library not supported by ds-express-errors? No problem. Use the customMappers config to teach the error handler how to process new error types without waiting for a package update.