custom-exceptions.js

// Proper exceptions in JS:

function MakeErrorClass(name, parent) {
  parent = parent || Error
  var cls = function(message) {
    parent.call(this, arguments)
    if (Error.captureStackTrace)
      Error.captureStackTrace(this, this.constructor)
    else
      this.stack = [name].concat(Error().stack.split('\n').slice(3)).join('\n')
    this.message = message
    Object.freeze(this)
  }
  cls.prototype = Object.create(parent.prototype, {name: {value: name, enumerable: true}})
  cls.prototype.constructor = cls
  return cls
}

// Example:
var MyError = MakeErrorClass('MyError')
var SubError = MakeErrorClass('SubError', MyError)

try {
  throw new SubError('foo')
} catch (e) {
  console.log(e instanceof MyError ? 'Got a MyError!' : 'Got an unknown error!')
}