Skip to main content

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 '@palla/config';

// uses 1000 if there is no `FOO` env variable available
const provider = new DefaultValueProvider(


Transforms value (if available) using provided transforming function.

@pallad/config has few built-in transformers.

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

// for env variable FOO=world returns "WORLD"
const provider = new TransformProvider(
value => value.toUpperCase()

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({
paths: ['.env']

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

Default with transformer

Just simple helper to easily wrap any provider with default value and/or transformer.

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

const envProvider = env('FOO');

// returns just envProvider since there is no default or transformer

// returns envProvider wrapped with DefaultValueProvider
wrapWithDefaultAndTransformer(envProvider, {default: 'BAR'})

// returns envProvider wrapped with DefaultValueProvider and TransformProvider
wrapWithDefaultAndTransformer(envProvider, {default: 'BAR', transform:})

// returns envProvider wrapped with TransformProvider
wrapWithDefaultAndTransformer(envProvider, { transform:})