express-error-factory

This is a simple custom error class and middleware for Express to better facilitate error handling in Express.

Usage

Installation

npm install express-error-factory

First, generate the custom errors using the CustomErrorThrower class.

const customErrors = new CustomErrorThrower({
    rodentError: {
        tooManySquirrels: {
            {
                type: "rodentError",
                statusCode: 400,
                message: "The squirrels have chewed all of your cables."
            }
        },
        possumKingdom : {
            type: "rodentError",
            statusCode: 500,
            message: "The opossums have decreed that your realm is now theirs."
        }
    },
    insectError : {
        bees: {
            type: "insectError",
            statusCode: 404,
            message: "Bees?"
        }
    }
})

Errors can then be generated or thrown easily in any Express route.

For synchronous code, use the throwCustomError(errorType) method.

// generates a function to throw 'rodentError' errors 
const thrower = customErrors.throwCustomError("rodentError");

// throws an error with the information in the tooManySquirrels object.
thrower("tooManySquirrels");

For asynchronous code, promises, or try/catch blocks, pass the error generated from the getErrorResponse(errorType) method to the Express next() function. For example:

// generates a function to create 'rodentError' errors
const createError = customErrors.getErrorResponse("insectError");

try {
    fetchDataFromApi();
} catch (error) {
    // do something to narrow error type to determine which custom error to throw
    next(createError("bees"));
}

See the Express documentation here for more information about the difference between syncrhonous and asynchronous errors.

Include the middleware as the last app.use(). The function can be given a custom error message for uncaught errors not specified in the CustomErrorThrower class.

app.use(authenticationMiddleware);

app.use(route1);
app.use(route2);

/*
.
.
.
*/

const errorMiddleware = handleCustomError("Uncaught Error Message");

app.use(errorMiddleware);

Github