determination

Configuration resolver. @vrbo/determination loads a JSON configuration file, resolving against criteria using confidence and shortstop protocol handlers.

In addition, @vrbo/determination supports javascript style comments in your JSON using shush.

Note: @vrbo/determination borrows heavily from confit, but prefers confidence for resolving environment as well as other criteria for filtering.

Usage

const Determination = require('@vrbo/determination');

Determination.create(options)

• options (Object) - an options object containing:
  • config (String | Object) - required, either a path to a JSON configuration file or an object.
  • basedir (String) - optional path used for resolving relative imports within configs. If config is a file, it defaults to the config file's directory. If config is an object, it defaults to process.cwd().
  • criteria (Object) - optional resolution criteria. See confidence. Minimally will always contain process.env under the key env.
  • protocols (Object) - optional mapping of protocols for shortstop. Protocols are bound with context config, where config is the configuration being resolved. Obviously this doesn't work with arrow functions.
  • defaults (Object | String) - optional default pre-resolved configuration values.
  • overrides (Object | String) - optional override pre-resolved configuration values.
• returns - a resolver.

resolver.resolve([callback])

• callback (Function) - an optional callback.
• returns - a promise if callback is not provided.

const Determination = require('@vrbo/determination');
const Path = require('path');
const Handlers = require('shortstop-handlers');

const config = Path.join('.', 'config', 'config.json');

const resolver = Determination.create({
    config,
    protocols: {
        require: Handlers.require(Path.dirname(config))
    }
});

resolver.resolve((error, config) => {
    // config.get
    // config.set
});

Config API

• get(string: key) - returns the value for the given key, where a dot-delimited key may traverse the configuration store.
• set(string: key, any: value) - sets the given value on the given key, where dot-delimited key may traverse the configuration store.
• merge(object: value) - merges the given value into the configuration store.
• use(object: store) - merges the given store into the configuration store.
• data - accessor for a clone of the underlying store data (modifying this will not modify store).

config.set('some.key.name', 'value');
config.merge({
    some: {
        key: {
            other: 'another value',
        },
    },
});
config.get('some.key.other'); // 'another value'

Shortstop Protocol Handlers

Two protocol handlers are enabled by default:

• import:path - merges the contents of a given file, supporting comments (unlike require).
• config:key - copies the value under the given key (supporting dot-delimited) to the key it is declared on.

Custom Protocol Handlers

An example of utilizing a custom protocol handler is below. This takes advantage of the context bound to the handler.

config.json

{
    "thing1": "one",
    "thing2": "two",
    "things": "eval:${thing1} and ${thing2}"
}

and

const Determination = require('@vrbo/determination');
const VM = require('vm');

const protocols = {
    eval(expression) {
        return VM.runInNewContext('`' + expression + '`', this);
    }
};

Determination.create({ config: Path.join(__dirname, './config.json'), protocols }).resolve((error, config) => {
    config.get('things'); // "one and two"
});

Resolution Order

Configuration file contents are resolved in the following order:

1. Resolve defaults against protocols.
2. Merge defaults with config.
3. Resolve merged config against protocols.
4. Resolve overrides against protocols.
5. Merge overrides into config.
6. Resolve config against config: protocol.