Validator

README.md

Environment Validation & Configuration

The validator (./lib/env/validator.js) is reponsible for handling and validating environment variables. The schema listed in ./lib/env/schema.js defines which variables are required, what are their defaults, which regex pattern is required and how to transform the passed values.

For this purpose the schema is an object of objects with the following properties:

• name <string>
  Define the name of the instance variable which exposes the transformed value.
  E.g. name="port" enables access via env.port.

• [required=false] <boolean>
  Define if a environment variable is required.
  Throws an error in case of undefined.

• [desc=''] <string>
  Short escription of the related variable. Should be provided for a object even though its not required. It enriches the error messages which further details.

• [default=undefined] <*>
  The default value of the variable.
  Is only mindful in the case of optional ones.

• [pattern=undefined] <RegExp>
  The pattern which validates the value of a defined variable. Has no effect in case of undefined.
  Throws an error in case of failure.

• [transform=undefined] <Function>
  A function which transforms the value (or default).
  The function receives the value a first argument and is required to return a new value.

  Example:

  {
    name: 'port',
    default: '3000',
    transform(x) {
      return parseInt(x, 10)
    }
  }

  This definition allows access to the port parsed as integer via env.port.

• [props=undefined] <Object.<Function>>
  An object of function which behave like transform but enable various representations of a single variable.
  It is not possible to define both props and transform.

  Example:

  {
    name: 'users',
    props: {
      list(x) {
        return x.split(' ')
      },
      raw(x) {
        return x
      }
    }
  }

  This definition allows access to a split string via env.users.list and the original string via env.users.raw.

index.js

const Validator = require('./validator')
const schema = require('./schema')

module.exports = new Validator(schema)

validator.js

module.exports = class Validator {
  constructor (schema) {
    Object.keys(schema).forEach((key) => {
      const def = schema[key]
      let value = process.env[key]

      if (def.props && def.transform) {
        throw new Error(`Use either 'props' or 'transform' on '${key}'.`)
      }

      if (def.required && value === undefined) {
        throw new Error(`Please provide ${def.desc} as '${key}'.`)
      }

      if (def.pattern && value !== undefined && !value.match(def.pattern)) {
        throw new Error(`Please provide format the '${key}' variable like listed in the docs.`)
      }

      value = value === undefined ? def.default : value

      if (def.transform) {
        value = def.transform(value)
      }

      this[def.name] = value

      if (def.props) {
        this[def.name] = {}

        Object.keys(def.props).forEach((prop) => {
          this[def.name][prop] = def.props[prop](value)
        })
      }
    })
  }
}