A simple configuration system allowing multiple configuration layers






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A simple configuration system allowing multiple configuration layers (e.g. defaults, user-defined config)

Each layer is treated independently. If the configuration is queried, all layers are scanned from the layer with the highest priority to the one with the lowest. The first layer that can resolve the queried path will be the one returning the configured value.


By default, an instance of LayeredConfiguration is created when the module is required.

// Load a ready-to-use LayeredConfiguration instance
let config = require('layered-config');

// If you want to create your own instance, use this instead:
let LayeredConfig = require('layered-config').LayeredConfiguration;
let myConfig = new LayeredConfig();

Adding layers

Before any configuration values can be read or written, we need to add one or more layers to the configuration.

If added by using addlayer(), every new layer will have a higher priority than the ones that were added before.

// Add a first layer including some data
        one: 1,
        two: 2,
        three: {
            foo: 'bar'

// Add another layer
// This one has a higher priority than "layerOne"
        three: {
            foo: 'overwritten', // This value overwrites the one in layerOne
            bar: 'baz'

console.dir(config.getLayerNames()); // ["layerTwo", "layerOne"]

getLayerNames() returns the names of the layers inside the configuration ordered from highest to lowest priority.

Querying data

Each value inside the configuration hierarchy can be addressed by using a configuration path that describes the position you want to access. By default, configuration paths use "." as separator. To get the value of "bar" in our example above, the corresponding configuration path would be

Querying the configuration is done by using get():

let valueOfBar = config.get('');
console.log(valueOfBar);                  // Output: 'baz'

// This will output "overwritten", since layerTwo has the highest priority

If you want to query data from a specific layer, just add the layer name as second parameter:

console.log(config.get('', 'layerOne')); // Output: 'bar'

You can even change the priority by passing the layer names in the order they should be queried:

console.log(config.get('', ['layerOne', 'layerTwo'])); // Output: 'bar'

Writing data

Data is written to the config using the set() method. It takes up to three parameters: The path to write to, the value to write and the layer the value shall be stored in. If the layer name is omitted, the new value will be written into the layer with the highest priority:

config.set('', 'This is my value'); // Writes to "layerTwo"

config.set('', 'Hello', 'layerOne'); // Writes to "layerOne"

You can write complete object hierarchies, too:

config.set('', {hello: {world: '!'});

let value = config.get('');
console.log(value); // Output: '!'

Loading configuration data

From the filesystem

layered-config reads and writes its configuration data using Hjson. This way, the configuration files can be written in a little bit more relaxed way and contain - for example - comments.

For more information about Hjson, see the Hjson website.

You can choose to either load each layer one by one using loadFromFile() or to fill the whole configuration by reading all .json and .hjson files from a directory using loadFromDirectory(). Both function return Promises that resolve when the load operations have completed.

// Load the contents of userData.hjson into a new layer named "userData"
    .then(/* ... */);

// Load the same file into a layer named "foo"
config.loadFromFile('./data/userData.hjson', 'foo')
    .then(/* ... */);

// Cleanup

// Load all (h)json files from ./data into the configuration
// Files will be loaded in alphabetical order
    .then(/* ... */);

// Assuming that the directory contains the files "foo.hjson", "bar.json" and "baz.hjson",
let names = config.getLayerNames(); // ["foo", "baz", "bar"]

If both, a .hjson and a .json file exist having the same filename, the resulting configuration will only contain the data from the .json file, because it will be loaded after the .hjson one, thus overwriting its data.

From environment variables

You can also load configuration data from environment variables using loadFromEnv(). This function takes an option object which configures the way, the environment variables are processed.

The available options are:

  • lowerCase (Boolean): convert environment variable names to lowercase? (default: true)
  • separator (String): if set, the variable name will be split into a path using the separator (default: '_')
  • whitelist (String[]): if set, only the variables inside this array will be loaded into the layer (default undefined)
  • match (regex): if set, only variables that match the regular expression will be loaded into the layer (default: undefined)

If neither whitelist nor match are set, all environment variables will be imported into the configuration layer.

// Add a layer containing process.env variables
// If no layer name is given, a new layer named 'process_env' will be created

Saving configuration data into files

When saving the configuration data you can either write the data of one layer into a single file using saveToFile() or write the data of all layers into Hjson files inside a directory, each having the layers' name by using saveToDirectory().

Just like the load methods, each save method returns a Promise.

When using saveToDirectory(), only those layers will be written to disk that have their writeToDisk property set to true (default: false).

// Add some layers with data
config.addLayer('one', {a: 1}).writeToDisk = true;
config.addLayer('two', {b: 2});
config.addLayer('three', {c: 3}).writeToDisk = true;

// Write layer "two" to disk
config.saveToFile('two', 'myConfigFile.hjson')
    .then(/* ... */);

// This will write layers "one" and "three" to the target directory
    .then(/* ... */);

// The "data" directory now contains the files "one.hjson" and "three.hjson"

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