Explicit error messages with VError

Today I will present you one of my favorite NPM modules. VError makes your errors more explicit.

I will not expose all the features here and just explain why I think this module is very useful. So don't hesitate to read the official documentation here

The thing I like with VError is the feature of building a composite error message through all applicative layers the error goes through.

Let see an example :

const VError = require('verror')

function model(json) {
  return JSON.parse(json)
}

function controller(json) {
  try {
    model(json)
  } catch (err) {
    const error = new VError(err, 'Model fail to parse json')
    throw error
  }
}

function routeHandler(rawJSON) {
  try {
    const data = controller(rawJSON)
    return data
  } catch (err) {
    const error = new VError(err, 'Controller fail to use json')
    throw error
  }
}

routeHandler('invalid json')

This script will generate the following error message :
VError: Controller fail to use json: Model fail to parse json: Unexpected token i in JSON at position 0

This is much more explicit to see than : SyntaxError: Unexpected token i in JSON at position 0

Also you can add some contextual information for each VError layers and get them at the end with the VError.info() function see documentation here

Examples :

const error = new VError({
  name: 'SERVICE_UNAVAILABLE',
  info: { json: rawJSON },
  cause: err,
}, 'Controller fail to use json')

console.log(VError.info(error)) // { json: 'invalid json' }
console.log(error.name) // SERVICE_UNAVAILABLE

Let me know in the comments if you use it already or if you will in the future and what are your feedbacks about VError.

Comments

[Zameer Fouzan]

i want to use this to throw & rethrow multi-level / multi-module errors , exclusively for retaining stacktrace.

brief summary:
I have 3-4 modules , and a custom error type.
if an error happens in module 4, i want to bubble the same to module 2 with the stack trace intact.

will this work for me ? are there any examples for this ?