response-catcher

Easy async error handling in Express

1npm install --save response-catcher

Introduction

response-catcher is an extremely flexible .catch() error handler for promise-based express request flows.

It should be used where you would have multiple .then() operations in a request and need to be able to throw and handle many kinds of errors.

By default it attaches itself to res.error() (though this can be configured).

Usage example

1const express = require("express");
2const app = express();
3
4const responseCatcher = require("response-catcher");
5app.use(responseCatcher());
6
7app.get("/", (req, res) => {
8	findUser()
9		.then(checkUser)
10		.then(andThenThisThing)
11		.catch(res.error());
12
13	async function findUser() {
14		let user = await db.users.find(req.body.id);
15		if (!user) throw 404;
16
17		return user;
18	}
19
20	async function checkUser(user) {
21		if (!user.isAuthenticated) throw [401, "User is not authenticated"];
22		else if (user.alreadyExists) throw ["User already exists", 409];
23		else if (user.username.length > 8) throw "Username is too long";
24		else if (serverErrorSomewhere) throw { status: 500, body: "Sorry, we had an error somewhere!" };
25	}
26
27	async function andThenThisThing() {
28		// ...
29	}
30});

Configuration

Instantiation

On instantiation of the middleware function, you can set the following properties (with the listed values being the defaults):

1{
2	name: "error", // The name of the function to use: "res.error()"
3	status: 400, // The default response status to use
4	logger: console.log, // The logging function to use for errors
5	logging: false // Whether or not to log errors
6}

To use a custom logger that isn't console.log, supply it to the logger key. This still won't enable logging, which to do set logging: true.

You can supply as many arguments as you like. Any string you provide will interpreted as the name, any number you use will be interpreted as the status, and any object you use will have the named properties.

1const responseCatcher = require("response-catcher");
2
3app.use(responseCatcher()); // Use the default values
4app.use(responseCatcher(405)); // Change the default status to 405
5app.use(responseCatcher({ logger: console.log })); // Enable logging
6app.use(responseCatcher("handleError", { status: 500 })); // Change both the default function name and the status

Creating the error

Coming soon...

Ways to throw an error

Coming soon...