dvar

dvar is a configuration management library. It currently supports the following to provide the configuration:

• env (reading from process.env)
• file (reading from file)
• provided (provided in the code as json)
• http (getting from url)

Quick Links

• Install
• Usage
  • Quick start
  • Multiple config's
• Options
• Events
• Types
  • Provided
  • File
  • Env
  • Http
• Environment specific config
• Dynamic reloading
• Override
• Extensions

Install

npm install dvar --save

Usage

Quick start

const dvar = require('dvar')
dvar.configure([
    {type: 'provided', variables: {test: 123}}
  ], (err, res) => {
    console.log(res.get('test')) //<- prints 123
    console.log(res.all()['test']) //<- prints 123
})

Multiple config's

dvar takes an array of config's which makes it possible to provide config from multiple sources.

const dvar = require('dvar')
 
process.env.testEnv = 456
 
dvar.configure([
  {type: 'provided', variables: {test: 123}},
  {type: 'env'},
  {type: 'provided', variables: {anotherOne: 'someString'}}
], (err, res) => {
  console.log(res.get('test')) //<- prints 123
  console.log(res.get('testEnv')) //<- prints 456
  console.log(res.get('anotherOne')) //<- prints 'someString'
})

When the same variable is provided in different sources it will be overridden based on the array order (higher index will override lower).

const dvar = require('dvar')
 
dvar.configure([
  {type: 'provided', variables: {override: 'firstString'}},
  {type: 'provided', variables: {override: 'secondString'}}
], (err, res) => {
  console.log(res.get('override')) //<- prints 'secondString'
})

Options

It is possible to provide a options object as the second parameter to the config function. If not provided defaults will be applied. The currently supported options are:

• replaceKeys: Takes a function and will apply it for every key, replacing it with a new key. The key will be passed as a parameter to the function and the new key must be returned.
• replaceValues: Same as replaceKeys for values.
• env: The current environment as a string or a function that returns the environment. Only used when providing config specific for certain environments as described here
• dynamic: Setting this option to a truthy value will enable dynamic reloading of the configuration. See more here

Example:

{
  replaceKeys: key => key.replace('-D', ''),
  replaceValues: values => String(value),
}

Events

The following events are emitted:

• loaded - Called when the config is finished loading. Passes the config values as a parameter.
• error - Called when there is an error reading from a provider. Passes the error as a parameter.
• updated - Called when the config is updated (i.e. when the dynamic reload interval passed). Passes the new config values as a parameter. This event is only fired when using dynamic reloading and will be called every time the config is reloaded no matter if the config actually changed from the reload.

Example loaded event:

const dvar = require('dvar')
dvar.once('loaded', values => {
  console.log(values.test) //<- prints 123
})
dvar.configure([{type: 'provided', variables: {test: 123}}])

Example error event:

const dvar = require('dvar')
dvar.once('error', err => {
  //...
})
dvar.configure([{type: 'file', path: 'does-not-exist'}])

Example updated event:

const dvar = require('dvar')
const fs = require('fs')
 
fs.writeFileSync('./testFile', 'testKey=testValue')
 
dvar.once('updated', values => {
  console.log(values.testKey)  //<- prints dynamicallyChangedtestValue
})
 
dvar.configure([
  {type: 'file', format: 'property', path: './testFile'}
], {
  dynamic: {
    interval: 10
  }
}, (err, res) => {
  fs.writeFileSync('./testFile', 'testKey=dynamicallyChangedtestValue')
})

Types

Provided

const dvar = require('dvar')
 
dvar.configure([
  {type: 'provided', variables: {test: 123}}
], (err, res) => {
  console.log(res.get('test')) //<- prints 123
})

File

Currently there are two formats supported:

• json
• property (key=value separated by new line)

const dvar = require('dvar')
const fs = require('fs')
 
fs.writeFileSync('./app.env', `testKey=testValue`)
 
dvar.configure([
  {type: 'file', format: 'property', path: './app.env'}
], (err, res) => {
  console.log(res.get('testKey')) //<- prints 'testValue'
})

Env

const dvar = require('dvar')
 
process.env.testEnv = 456
 
dvar.configure([
  {type: 'env'}
], (err, res) => {
  console.log(res.get('testEnv')) //<- prints 456
})

HTTP

Currently there are two supported formats, that can be passed in the http response:

• json
• property (key=value separated by new line)

const dvar = require('dvar')
const http = require('http')
 
http.createServer(function(request, response) {
  response.end(`testKey=testValue`)
}).listen(8080)
 
dvar.configure([
  {type: 'http', format: 'property', url: 'http://localhost:8080/test'}
], (err, res) => {
  console.log(res.get('testKey')) //<- prints 'testValue'
})

Environment specific config

Instead of providing an array to the config function, it is also possible to pass an object to it. The key(s) should be the environment for which the config is and the value the actual config array. Further, it is possible to provide an option env that is used to determine the current environment that should be used. It can be either a string or a function that returns a string with the environment.

dvar.configure({
  staging: [{type: 'provided', variables: {staging: 123}}],
  production: [{type: 'provided', variables: {prod: 123}}]
}, {
  env: () => {
    return 'staging'
  }
}, (err, res) => {
  console.log(res.get('staging')) //<- prints 123
})

Dynamic reloading

Dynamic reloading of the configuration can be enabled by setting the dynamic option to a truthy value. By default it will poll for configuration changes every minute. When setting the dynamic field to a object, an interval option (in ms) can be passed to it.

const dvar = require('dvar')
const fs = require('fs')
 
fs.writeFileSync('./testFile', 'testKey=testValue')
 
dvar.configure([
  {type: 'file', format: 'property', path: './testFile'}
], {
  dynamic: {
    interval: 10 //in ms
  }
}, (err, res) => {
  console.log(res.get('testKey')) //<- prints testValue
 
  fs.writeFileSync('./testFile', 'testKey=dynamicallyChangedTestValue')
 
  setTimeout(() => {
    console.log(res.get('testKey')) //<- prints dynamicallyChangedTestValue
  }, 12)
})

Override

Override is a function that takes a config the same way as configure. When using that function all subsequent calls to configure will use the configuration defined in the override function instead of it's own. This is useful for testing, when a specific test configuration is needed. Calls to configure before the override function is called won't be affected.

const dvar = require('dvar')
 
dvar.override([
  {type: 'provided', variables: {test: 123}}
], (err, res) => {
  console.log(res.get('test')) //<- prints 123
 
  dvar.configure([
    {type: 'provided', variables: {test: 456}}
  ], (err, res) => {
    console.log(res.get('test')) //<- prints 123
  })
})

To remove a override config there is a function removeOverride. This will cause all subsequent calls to configure to use their own configuration instead of the one provided by override. The configure calls done before the removeOverride will still use the override configuration though.

Extensions

Additional providers can be added using extensions.

const dvar = require('dvar')
 
dvar.addExtension('myExtension', {init: (config, cb) => {
  const readF = cb => cb(null, {test: 123})
  cb(null, {read: readF})
}}).configure([
  {type: 'myExtension'}
], (err, res) => {
  console.log(res.get('test')) //<- prints 123
})

As you can see in the example the addExtension function takes the name of the extension and the actual extension / provider. The extension must have a init function that takes the config (As defined in the configure call) and a callback function. On success the callback function must return another function read that will read the configuration.