The catchAsync Function

catchAsync is a utility function in the Arkos that wraps asynchronous request handlers and middleware to automatically catch errors and forward them to Express's error handling mechanism. This eliminates the need for repetitive try-catch blocks in every route handler, creating cleaner code and ensuring consistent error handling.

tip

You can use the function even to catch non async errors by simply letting the function throw it.

Purpose

The catchAsync function serves several important purposes:

1. Error Propagation: Automatically forwards errors to Arkos's global error handler (built on top of Express global erro handler).
2. Code Cleanliness: Eliminates repetitive try-catch blocks in route handlers
3. Preventing Unhandled Rejections: Ensures all Promise rejections are properly caught
4. Centralized Error Handling: Works with AppError to create a cohesive error management system, read more about AppError.
5. Developer Experience: Reduces boilerplate code and potential for human error

As you are reading about the catchAsync maybe you may want to also read about the Arkos Global Error Handler clicking here.

Function Signature

const catchAsync =
  (fn: ArkosRequestHandler) =>
  async (req: ArkosRequest, res: ArkosResponse, next: ArkosNextFunction) => {
    try {
      await fn(req, res, next);
    } catch (err) {
      next(err);
    }
  };

Parameters

Parameter	Type	Description
fn	ArkosRequestHandler	The async Express/Arkos route handler or middleware function to be wrapped

Return Value

Returns a new async function that:

1. Takes the ArkosRequest, ArkosResponse and ArkosNextFunction extended from Express parameters (req, res, next)
2. Calls the original function within a try-catch block
3. Forwards any caught errors to Arkos's error handling middleware using next(err)

Usage Examples

Basic Route Handler

import { ArkosRequest, ArkosResponse, ArkosNextFunction } from "arkos";
import { catchAsync } from "arkos/error-handler";
import { prisma } from "../../utils/prisma";

// Without try-catch boilerplate
export const getAllUsers = catchAsync(async (req, res, next) => {
  const users = await prisma.user.findMany();

  res.status(200).json({
    status: "success",
    results: users.length,
    data: { users },
  });
});

As shown below you do not need a try-catch block when using catchAsync, neither forwarding the error to global handler nor even about throwing errors sometimes (Just if you would like a specific message), why??? because Arkos handles it for you by providing a set of meaningfull error messages and status code. read more about

With Custom Error Throwing

import { ArkosRequest, ArkosResponse, ArkosNextFunction } from "arkos";
import { catchAsync } from "arkos/error-handler";
import { prisma } from "../../utils/prisma";

export const getUserById = catchAsync(
  async (req: ArkosRequest, res: ArkosResponse, next: ArkosNextFunction) => {
    const user = await prisma.user.findOne({ where: { id: req.params.id } });

    if (!user) {
      throw new AppError("User not found", 404, { userId: req.params.id });
    }

    res.status(200).json({
      status: "success",
      data: { user },
    });
  }
);

In Middleware

import { ArkosRequest, ArkosResponse, ArkosNextFunction } from "arkos";
import { AppError, catchAsync } from "arkos/error-handler";

export const protectRoute = catchAsync(
  async (req: ArkosRequest, res: ArkosResponse, next: ArkosNextFunction) => {
    // Get token from request headers
    const token = req.headers.authorization?.split(" ")[1];

    if (!token) {
      throw new AppError("Not authenticated. Please log in.", 401);
    }

    // Verify token
    const decoded = await verifyToken(token);

    // Add user to request object
    req.user = decoded;

    // Continue to next middleware/handler
    next();
  }
);

info

Rember that many of the examples mentioned above are alreday handled my Arkos behind the scenes for these are basic errors, this way you can focus on what really matters.

Error Handling Flow

When using catchAsync, the error handling flow works like this:

1. Your route handler or middleware executes inside the try block
2. If an error occurs (throw or Promise rejection), it's caught automatically
3. The error is passed to Express's next function
4. Express forwards the error to your global error handling middleware
5. The global error handler processes the error (ideally checking for AppError instances)

Benefits

Why Use catchAsync?

1. DRY Principle: Eliminates repetitive try-catch blocks across your codebase
2. Reliability: Ensures no async errors are missed or unhandled
3. Consistency: All errors are channeled through the same error handling process
4. Readability: Makes route handlers cleaner and focused on business logic
5. Maintainability: Centralizes error handling logic in one place

Integration with AppError

catchAsync works best when paired with the AppError class, read more about the AppError class:

import { AppError, catchAsync } from "arkos/error-handler";
import { ArkosRequest, ArkosResponse, ArkosNextFunction } from "arkos";

// Controller function
export const updateUser = catchAsync(
  async (req: ArkosRequest, res: ArkosResponse, next: ArkosNextFunction) => {
    // Validation
    if (!req.body.name && !req.body.email) {
      throw new AppError("Please provide name or email to update", 400);
    }

    // Business logic
    const updatedUser = await User.findByIdAndUpdate(req.params.id, req.body, {
      new: true,
      runValidators: true,
    });

    // Resource check
    if (!updatedUser) {
      throw new AppError("User not found", 404, { userId: req.params.id });
    }

    // Response
    res.status(200).json({
      status: "success",
      data: { user: updatedUser },
    });
  }
);

Best Practices

1. Wrap All Async Handlers: Use catchAsync for all async route handlers and middleware
2. Paired with AppError: Throw AppError instances inside your wrapped functions
3. Express Setup: Make sure you have a global error handler middleware registered
4. Error Specificity: Throw specific errors with appropriate status codes
5. Clean Architecture: Consider creating service layers wrapped with their own error handling