envconf

This module makes it easy to use express-style configuration for any application. It allows your users to define separate configuration environments in code and switch between sets of configuration via a single environment variable.

Basic Usage

var envconf = require('envconf');

var c = envconf.createConfig();

c.configure('development', function (c) {
  c.set('settingOne', 'devValue');
});

c.configure('production', function (c) {
  // You can also pass in an object literal to set a bunch
  // of values at once
  c.set({
    settingTwo: 'prodValue'
    prodOnly: 'prodSpecific'
  });
});

c('development').get('settingOne').should.equal('devValue');

process.env.NODE_ENV = 'production';
c.default.get('settingTwo').should.equal('prodValue');
c.default.get('prodOnly').should.equal('prodSpecific');

The previous code shows picking up the default environment from the NODE_ENV environment variable.

You can however configure your own environment variables as shown below.

var c2 = envconf.createConfig({ defaultEnvVar: 'MY_LIBRARY_VAR'});

c2.configure('development', function (c) {
  c.set('settingOne', 'devValue');
});

c2.configure('production', function (c) {
  c.set('settingTwo', 'prodValue');
});

c2('development').get('settingOne').should.equal('devValue');

process.env.MY_LIBRARY_VAR = 'production';
c.default.get('settingTwo').should.equal('prodValue');

Setting Getters

Instead of a setting a simple value, you can instead use the setFunc method to provide a function that will run when the value is requested:

var c2 = envconf.createConfig();

c2.configure('development', function (c) {
  c.setFunc('settingOne', function () { return 'This value came from a function'; });
});

c2.get('settingOne').should.equal('This value came from a function');

or, if you use the object literal version of set, values that are functions will be treated as if you called setFunc for that value:

var c2 = envconf.createConfig();

c2.configure('development', function (c) {
  c.set({
    settingOne: function () { return 'This value also came from a function'; }
  });
});

c2.get('settingOne').should.equal('This value also came from a function');

This can be handy if you want to have a default value that you need to derive from ambient state.

Customizing the config object

Do you want to add helper methods for your specific configuration? Or set specific values in every configuration? It's easy with a config customizer:

function addConfigHelpers(config) {
  config.useSql = function (host, db) {
    config.set('sql host', host);
    config.set('sql database name', db);
  }
}

var c3 = envconf.createConfig( { customizer: addConfigHelpers });

c3.configure('test', function (c) {
  c.useSql('testmachine', 'testdb');
});

c3.configure('production', function (c) {
  c.useSql('realDatabase', 'actualDb');
});

// Can also customize after creation, customizations
// will affect any child configs too!
c3 = envconf.createConfig();
var prod = c3('prod');

c3.customize(addConfigHelpers);

c3.configure('production', function (c) {
  c.useSql('realDatabase', 'actualDb');
});

Saving and Restoring config values

Are you making changes to a global configuration in your unit tests, and want to ensure you've restored the state after your test? Use a snapshot:

var c4 = envconf.createConfig();
c4.configure(function (c) {
  c.set('originalValue', 'one');
});

// set up contents of c4

var snapshot = c4.snapshot();

c4.configure(function (c) {
  c.set('originalValue', 'two');
});

c4.restore(snapshot);

c4.get('originalValue').should.equal('one');

Snapshot/restore also saves and restores any child configurations.

Temporary Configs

Similarly, you might want to set up a configuration and then be able to throw it away without giving it a name. Easy:

var c5 = envconf.createConfig();
c5.configure(function (c) {
  c.set('originalValue', 'one');
});

var c6 = envconf.tempConfig();
c6.set('tempValue', 'temp');

// You can look up values in the temp config or the parent
c6.get('tempValue').should.equal('temp');
c6.get('originalValue').should.equal('one');

// But the parent has no record of the temp
c5.environments.length.should.equal(0);