Custom Error Handling in Node with Promises

application-errors.js

module.exports = {
  ValidationError: class extends Error{
    constructor(message){
      super(message || "This input is invalid")
    }
  },
  DatabaseError: class extends Error {
    constructor(message){
      super(message || "The database call failed")
    }
  },
  OtherError: class extends Error {
    constructor(message){
      super(message || "Something else happened")
    }
  }
};

async-file.js

const Promise = require("bluebird");
const fs = require('fs');
const e = require('./application-errors');
Promise.promisifyAll(fs);
   
function processNewlines(data){
  console.log(data.split('\n').length - 1);
  return Promise.reject(new e.ValidationError("processNewlines broke!"));
}

fs.readFileAsync(process.argv[2], 'utf8')
.then(processNewlines)
.catch( e.ValidationError, function(e){
   console.error(e);
});