Unmarshaller

Toolbox for configuration

Motivations

• A declarative way for defining configuration
• Reusability and composability
• Flexible and generic

Installation

npm install --save unmarshaller

Example

import {builder, unmarshal} from 'unmarshaller';

const unmarshaller = {
  editor: builder.string('EDITOR'),
  browser: builder.string('BROWSER'),
};

const lookupFn = (key) => process.env[key];
const config = unmarshal(lookupFn, unmarshaller);

console.log(config);

Basics

Lookup function

You need to provide to the unmarshal function a way to lookup from keys in configuration.

The example above returns the value found in the process's environment:

const lookupFn = (key) => process.env[key];

Unmarshaller

Just an object which represents your configuration.

Builder

Helper functions to build the unmarshaller object.

Default types

| type | |---------| | string | | boolean | | number | | object | | holder | | or |

Default options

|name|type|description| |----|----|-----------| |defaultValue|string|fallback value if the lookup returned undefined or null| |of|array|provide an enumeration of possible values| fallbacks to defaultValue and null.| |parser|function|provide an custom parser function (usually when you want your own types)|

Or

const unmarshaller = {
  foo: builder.or(
    builder.string('foo_a'),
    builder.string('foo_b'),
  )
};

The unmarshalling process will call the lookup function until a value (not undefined or null) is returned.

Extending an existing holder

import {extend, builder} from 'unmarshaller';

const holder = builder.holder({
  editor: builder.string('EDITOR'),
  browser: builder.string('BROWSER'),
});

const extendedHolder = extend(holder, {
  version: builder.string('VERSION'),
});

Extending the default builder

The builder is a regular JavaScript object.

Customizing the builder gives you the possiblity to use your own data converters.

The following example use a custom type: color (which in my use case parses a string into a structure).

import {builder as defaultBuilder} from 'unmarshaller';

export const builder = {
  ...defaultBuilder,
  color: (name, options) => ({
    name,
    parser: parseColor,
    type: 'color',
    ...options
  }),
};

You need to provide a custom parser function (parseColor in the example above). The definition is: function(value: string): string.