1.5.0 • Public • Published


The ultimate configuration library, has it all in. Last one you ever going to use.

The module takes care of configuration options discovery, parsing and merging. Just put your config files into the config folder – and you're done!

global/local/prod/qa/etc. config files, environment variables, command line options, hardcoded and default values – all is taken care of.

json, js, json5, yaml, ini – pick your configuration language and lastconf will just take it.


npm i lastconf -S



  port: 4321
const conf = require("lastconf")();"database host:", conf.get(""));

i.e. to initialize config call exported object upon require as a function or call init(optionalOptionsObject, optionalHardcodedObject) on it later.

Typicaly your config folder should include the following:

  • config.json5 - some defaults
  • config.development.json5 – overwrites pointers to db/api/whatever remote services to local ones
  • config.test.json5 – a set of variables used for testing
  • config.local.json5 - totally local stuff, this file should never be checked in.

Note: if environment is explicitly set (say, NODE_ENV=TEST), local settings from config.local.json5 are ignored. But vars from environment and command line still takes precedence.


const conf = require("lastconf")(options, hardcodedValuesObject);

where options are:

  • default – object with initial params, likely to be overwritten.

  • separator - what separates multi-level keys, like in Default is .

  • environmentSeparator - same as above, but for the environment vars. Default is __

  • folder – directory where all config files supposed to be located. Default is config. If location option is not specified, path will be relative to where teh script is run from. Can be compound, as "src/config".

  • location - where folder with config files to be found. By default it is where the script is run from (project, top level folder). If it is script, then main script location-related. I.e. if your script is located in some sub-folder, config folder should be at the same level.

  • debug a bit of info as to where the config files are read from and which ones are read and in what order.

and hardcodedValuesObject is just a hash that will overwrite anything. Useful for quick'n'dirty temporary changes to test something.


  • All keys internally a lowerkeyed. As such, .get("SomeKey") function can take whatever, but turn the key to lowercase. So, "SOMEKEY", "sOmEkEy" and "someKey" will be treated as "somekey".

  • Priority sequence:

    • options.defaults parameter
    • configs from files
    • command line options (not implemented, not sure if anyone really needs it)
    • environment vars
    • hardcoded parameters
  • Note to environment vars: lastconfig will attempt to only extract keys that have been extracted and placed into config object already. I.e. if you plan to use "DATABASE" env var, specify it in one of the configs or in defaults parameter, as { database: null }.

  • Files in order:

    • config
    • config.local -- never checked in.
    • config.<NODE_ENV>
    • config.<NODE_ENV>.local -- never checked in.

i.e, for the development:

  • config.json
  • config.local.json
  • config.development.json
  • config.development.local.json

and for test:

  • config.json
  • config.local.json
  • config.test.json
  • config.test.local.json

as it is seen, the first two configs are common, and the last two differ.

  • Extensions for each file to try in order:
    • json
    • json5
    • js
    • yaml
    • ini

-- if all developers configure their machines alike, there'll be no need for the dedicated config.local file.

Sensible defaults

  • Config folder: ./config
  • keys separator: .
  • environment variable keys separator: __

using the environment variables

env vars are processed and placed into the config object tree after all config files are processed; but the processor needs to know which of the env vars to take and process. So for each env var processor will look in the built tree to find the match. In other words, the key should exist in config for the env var to be processed. So either define needed keys in the config.js, values might be null or whatever or just pass the defaults object while initializing the lastconf.

config files location

By default, it will look for files in ./config folder from where the app is launched, typically, project root. Name of the folder is controlled by a folder option (i.e. config by default). Location of this config is controlled by a location option: if it is defined as { location: "script" } this config folder will be relative to the location of the main script itself. Useful when several different scripts need to use different configs.

using config in different app modules

Since this lastconf is a singleton (by the nature of node modules), it needs to be configured once, likely, at the main app file, like so:

// main app:
const conf = require("lastconf")({
    separator: ":",
    debug: true,

after this point config is initialized and assembled. Any other modules now can simply get the reference to this config like so:

// some other module:
const conf = require("lastconf");

initializeDatabase(conf.get("database:config")); // note use of `:` – this separator was configured in the main app

Reading config values

    const key = config.get("simpleKey");
    const key = config.get("some.nested.value");

it can return whatever value is found on that key – simple scalar or a portion of config object, starting from that key

or get the whole config as an object:

    const conf = config.json();

or a portion thereof:

    const conf = config.json("some.nested");

which is essentially the same as config.get("some.nested"), really

resolving paths

The same config can be used by different apps from different folders. And if some config parameter needs to specify some relative folder, it might be a problem. it might be solved by making a relative path (relative to the config files location) using __dirname in the .js config file

    directory: __dirname + '/../db/migrations'

or by using a special resolvable placeholder %%%configFolder%%%:

    directory: '%%%configFolder%%%/../db/migrations',

which works for every other type of configs – .json, .yaml etc.

real world example

let's say a project requires knex config for running knex cli commands as well as a server that needs to have a database config. All is defined in a single servers/config/config.js file:

module.exports = {
  knex: {
    client: 'postgresql',
    connection: {
      database: 'projectdb-dev',
      user:     '',
      password: ''
    pool: {
      min: 2,
      max: 10
    migrations: {
      tableName: 'knex_migrations',
      directory: '%%%configFolder%%%/../db/migrations',
    seeds: {
      directory: '%%%configFolder%%%/../db/seeds'

knexfile.js is like so:

const conf = require("lastconf")({ folder: "servers/config" }).get("knex");

module.exports = {

and server.js have this snippet:

const config = require("lastconf")({ location: "script" });
const bookshelf = require("./bookshelf")(config.get("knex"));

and both scripts can be easily run from the project root:

knex migrate:rollback; knex migrate:latest; knex seed:run
nodemon servers/server.js


  • Currently, it throws an exception if config file contains an error for jsons only. Do the same for every other type.

  • validation or at least mandatory params check.

  • native error handling&reporting while parsing files – should informatively tell where the error was (kinda works for .js files now)

  • add a param that specify config file name to process in addition to standard ones (really needed?)

  • .has function (really needed?)

Other npms with similar functionality in no particular order:

  • nconf
  • node-config
  • dotenv (just treats env vars, won't allow for multiple configurations)

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  • nmakarov