determination
Configuration resolver using confidence and shortstop.
Last updated 7 months ago by tlivings .
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determination

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

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

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

Usage

const Determination = require('determination');

Determination.create(options)

  • options (Object) - an options object containing:
    • config (String) - required path to a JSON configuration.
    • 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('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('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.
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