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Composing providers

Embracing famous composition over inheritance advice, @pallad/config defines few hybrid providers for composition.

Default value​

Uses default value if injected provider's value is not available.

import {DefaultValueProvider, env} from '@pallad/config';

// uses 1000 if there is no `FOO` env variable available
env('FOO').defaultTo(1000);

Making value optional​

If value is not required you can default it to undefined by calling .optional().

env('FOO').optional();
// the same as
env('FOO').defaultTo(undefined);

Transform​

Transforms value (if available) using provided transforming function.

@pallad/config has few built-in transformers.

import {TransformProvider, env} from '@pallad/config';

env('FOO').transform(value => value.toUpperCase());
info

Using .transform() is a main way to ensure type safety since the inferred value type comes from return type of function passed to it. Use it in case of any problems with type inference.

First available​

Returns first available value. If non is available then fails. It's great for creating your own presets of providers.

import {env, FirstAvailableProvider} from '@pallad/config';
import {envFileProviderFactory} from '@pallad/config-envfile';

const envFile = envFileProviderFactory({
    files: ['.env']
});

// gets value from env variable FOO, if that is not available fallback to FOO from envfile
const provider = new FirstAvailableProvider(
    env('FOO'),
    envFile('FOO')
);