Yet another NodeJS JSON configuration loading library
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cfig - Configuration Manager

Yet another NodeJS JSON configuration loading + command-line argument parsing library. Because the world needed another and I've written this code too many times not to have it in a library.

The purpose is to provide a standard, straightforward way of reading configuration from configuration files and command-line arguments, and encapsulating that information.

A Configuration object has a name - which is the name of JSON files it will look for. By default it looks for $NAME.json in /etc, ~/ and ./ (but you can pass some other set of folders if you want). It will read all of them if all are present, with later ones overriding earlier ones.

Then it looks at the command-line arguments (e.g. --port 8080 or -p 8080) and includes those, possibly overriding values from files. You can supply expansions for single-letter command-line switches.


In a file called myapp.js:

        var Configuration = require( 'cfig' );

        var defaults = { foo : 'bar', baz : 42 }

        new Configuration( defaults, function(err, cfig) {

            // cfig now contains the defaults, overridden by values from
            // /etc/myapp.json, ~/myapp.json and ./myapp.json
            // overridden again by any command-line arguments in the form
            // --key value

Constructor arguments to Configuration can be supplied in any order; there can be any, none or all of:

  • An array of strings - directories to look in for JSON files, instead of /opt/local/etc, /etc/, ~/ and ./
    • As of 1.1, a string may also be an HTTP or HTTPS url to download configuration from
  • An object (non-array javascript hash) containing default values
  • A string - the name for those JSON files - if not, it uses the basename of require.main - i.e. it will be myapp.json if the main file is named myapp.js.
  • A boolean - if true, log the files it's reading as it reads them
  • A function - to call back once all files have been read
  • A joi schema object for validation (since v1.4.0)

What It Does

  • Loads configuration from JSON files and gives you back a Javascript object of them
  • By default, looks for $NAME.json in /etc, ~/ and ./ - that is
    • System-wide configuration in /etc
    • Per-user configuration in the current user home (if any)
    • Per-session configuration in the process working dir
    • Overrides any of those with command-line arguments
  • The file name is the file name of the file that launched the process, minus any .js
    • Unless you pass a string argument to the Configuration constructor
  • Iterates all command-line arguments (process.argv.slice(2)) and processes them, assuming a format --key value for long-form arguments. Configuration.addExpansions() allows you to provide a hash of short (e.g. -k) arguments and what long key names they should map to.

Command-Line Arguments

The process arguments are also taken into account. Say you want to allow short-form unix style arguments, which can be combined - i.e. -xvf is the same as -x -v -f is the same as --extract --verbose --file:

        var expansions = {
            x: 'extract',
            v: 'verbose',
            f: 'file'
        var defaults = { verbose : false }

        const Configuration = require('cfig').withExpansions(expansions);

        Configuration(defaults, function(err, cfig) {

If you pass -xvf you get

        extract : true,
        verbose : true,
        file : true

You can also customize the arguments passed, rather than getting process.argv.slice(2) applied:

        const Configuration = require('cfig').withExpansions(expansions, ['-x', '-v']);

        Configuration(defaults, function(err, cfig) {

Dot Notation

Cfig supports limited dot-notation in command-line arguments - that is, passing will get you { foo : { bar : true }}, but passing array offsets, e.g. --foo.1 is not supported.

Environment Variables

To allow environment variables to override configuration defaults, use the constructor function Configuration.withEnvironment() or Configuration.withEnvironmentAndExpansions() (the latter returns a function you call with the regular arguments) - your callback will receive a read-only object with getters for all keys defined in any defaults passed or configuration files read. Nested object properties are looked up in the environment as variables named outerName.innerProperty, so if you pass defaults such as { foo : { bar : 'baz'}} then an environment variable will override it.

A note on numbers: Environment variables are always strings; if the value that would be returned for a key, were environment variables not considered, is a number, and the value of the corresponding environment variable is parsable as an integer or floating point number, then it will be converted to a number.

Similarly, in the case of booleans, if the default value is a boolean and the environment variable is 0, false or FALSE it is converted to Javascript boolean false; if it is 1, true or TRUE it is converted to Javascript true; otherwise the string value of the environment variable is passed unaltered.


Command-line arguments are converted to booleans or numbers under the following conditions:

  • number - /^\d+/ matches the value
  • boolean - the strings 'true' or 'false' match the value


Configuration objects have one method: reload(callback), which can be used if you expect files on disk to be externally changed.

Note, this is a method on the return value from calling Configuration(), not the object with fields passed to the callback.

What's New

  • 2.0.0 - The object passed to the callback is no longer the same object returned/created by Configuration() - i.e. new Configuration (...) returns a Configuration object with a reload() method; the callback you pass to Configuration is not what is passed to the callback. The style of using Configuration() as a constructor is deprecated, since it was possible to see the object before all files were loaded and the properties fully populated with their final values. For the moment, after load, the returned object is populated with all of the same values once loading is complete. This behavior will be removed in 3.x.

  • 2.0.0 - Configuration.addExpansions() is deprecated - this altered the behavior of Configuration globally for all modules, which is a bad idea. It's replacement, withExpansions() offers the same functionality plus the ability to pass a second argument of command-line arguments (overriding use of process.argv) in one shot.

  • 2.0.0 - Configuration.child(name, expansions, args) - a method on the Configuration object, not the key/value pair object passed to the callback allows you to load a second set of configuration files and defaults and have them appear as a field of the original

  • 1.4.0 - Joi validation was added in 1.4.0, allowing a schema to be passed in for validation

  • 1.3.1 - Tests are moved to a new location