stolksdorf/egads

Yet another extensible error library for node.js

egads

Yet another extensible error library for node.js

Extensible, Generic, Agnostic, Descriptive, Simple

Why this library?

There are tons of alterntive libraries out there, however they didn't meet the feature set I wanted:

• Super tiny (under 40 lines!)
• Doesn't pollute global scope or mutate existing types
• Configurable and overwritable name, message, status, and custom fields
• Deep nesting. Each extended error can further extend
• Each error is an instanceOf all of it's parents, including the native Error type
• Don't have to use the new keyword when throwing
• Can use a single object parameter or multiple parameters
• Can access the error stack, eg. err.stack

How To Use

Install npm install egads

Define your errors.

//define your base error
var Err = require('egads').extend('Something done goofd', 500, 'GenericError');

//Extend it for cover you basic types
Err.auth = Err.extend('Unauthorized', 401, 'AuthError');

//Make specific errors
Err.auth.badToken = Err.auth.extend('Bad Auth Token');

//Use object parameters
Err.badInput = Err.extend({
    name : 'BadInputError',
    message : 'What am I suppose to do with this?',
    status : 400,
    fields : {
        shameOnYou : true
    }
})

module.exports = Err;

Throw'em

try{
    throw new Err.auth.badToken();
}catch(err){
    err instanceof Error;             //true
    err instanceof Err;               //true!
    err instanceof Err.auth;          //true!!
    err instanceof Err.auth.badToken; //true!!!
    
    err.name;       //'AuthError'
    err.message;    //'Bad Auth Token'
    err.status;     //401
    err.stack;      //Full stacktrace
    err.toString(); // 'AuthError : Bad Auth Token'
}

//Overide it!
try{
    //Leave out the `new` if you want
    throw Err.auth({
        status : 418,
        name : 'TeapotError',
        message : 'Entity body must be short and/or stout',
        fields : {
            type : 'Earl Grey',
            temp : 'hot'
        }
    });
}catch(err){
    err instanceof Err.auth;  //true!
    
    err.fields.type;          // 'Earl Grey'
    err.status;               //418
    err.toString();           // 'TeapotError : Entity body may be short and/or stout'
}

Express Handler

If you using express you can write a simple error handler for egads errors.

var app = require('express')();
var ApiError = require('egads');

var AuthError = ApiError.extend({
    status : 400,
    name : 'AuthError'
});

app.get('/:coolGuy', (req, res) => {
    if(!req.params.coolGuy) throw AuthError('not cool enough');
    return res.send('yo');
});

//Express Error Handler
app.use((err, req, res, next) => {
    if(err instanceof ApiError){
        //Since this is an API Error, we know it will have a status, name, and message
        return res.status(err.status).send({
            type : err.name,
            message : err.message
        });
    }
    //If a generic error, print the whole stack for debugging
    return res.status(500).send({
        message : err.message,
        stack : err.stack
    });
});