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    atrace-settings

    0.8.4 • Public • Published

    atrace-settings

    A minimal configuration library.

    Features

    • Convenient with Node and browser environments (WebPack, ...)
    • Validation for missing and invalid settings with informative errors
    • Tight types inferred with minimal boilerplate
    • Easy to test

    Quickstart

    Basic usage

    import {
      intSetting,
      invalidSource,
      settingsProvider,
      stringSetting,
    } from 'atrace-settings';
    
    const settings = settingsProvider((env) => ({
      port: intSetting(env.PORT ?? 8080), // Integer value
      auth: { // Hierarchical settings
        clientID: stringSetting(env.CLIENT_ID ?? 'my-client'), // String value
        clientSecret: stringSetting({
          source: env.CLIENT_SECRET ?? invalidSource, // Required string value
          sensitive: true, // Redact field from parsed sources
        }),
      },
      tag: stringSetting(env.TAG), // Optional string value
    }));
    
    const val = settings(); // Parsed values

    Importantly, val's type will automatically be inferred as:

    {
      readonly port: number;
      readonly auth: {
        readonly clientID: string;
        readonly clientSecret: string;
      }
      readonly tag: string | undefined;
    }

    If CLIENT_SECRET wasn't defined in the environment, the config provider will throw an informative exception.

    Defining a custom setting

    We provide a convenience factory builder for types which do not need any non-standard creation arguments.

    import {simpleSettingFactory} from 'atrace-settings';
    
    // A setting which will have values inferred as `Date`s.
    const dateSetting = simpleSettingFactory((s): Date => new Date(s));

    If additional arguments are desired, it's always possible--just more verbose--to use the underlying setting factory directly. For example, here's one way to implement an enum setting:

    import {
      newSetting,
      Setting,
      SettingParams,
      SettingSource,
    } from 'atrace-settings';
    
    /** Enum setting creation parameters. */
    export interface EnumSettingParams<E extends string, S>
      extends SettingParams<S> {
      /** Allowed enum values. */
      readonly symbols: ReadonlyArray<E>;
    }
    
    /** Creates a new enum setting. */
    export function enumSetting<E extends string, S extends SettingSource>(
      params: EnumSettingParams<E, S>
    ): Setting<S, E> {
      return newSetting(params, (s): any => {
        if (!~params.symbols.indexOf(s as any)) {
          throw new Error('Invalid enum value');
        }
        return s;
      });
    }

    Testing

    To test different setting values without needing mocks, pass in a custom environment when calling the config provider.

    const val = settings({
      CLIENT_ID: 'test-id',
      CLIENT_SECRET: 'test-secret',
    });

    Project structure

    In production code, we recommend using modular configuration types. Performing post-processing on setting values is easy with a settingsManager:

    // src/config.ts
    import {settingsManager} from 'atrace-settings';
    
    // First the (private) underlying settings resource manager.
    const withSettings = settingsManager((env) => ({/* ... */}));
    
    // Then the (public) configuration types. These can be different from the raw
    // settings for example discriminated unions are often handy. These are meant
    // to be used everywhere in the application. Smaller, more specific, types will
    // make testing easier and increase modularity.
    export interface ModuleAConfig {/* ... */}
    export interface ModuleBConfig {/* ... */}
    export interface Config {
      readonly moduleA: ModuleAConfig;
      readonly moduleB: ModuleBConfig;
      // ...
    }
    
    // Now the (public, though not meant for use everywhere - see below)
    // configuration factory. This function should only be imported in the
    // application's entry point and this module's unit-tests. Other modules should
    // accept already instantiated configuration types, making testing much easier
    // and dependencies explicit.
    export const config = withSettings((val) => {
      // Transform the setting values into the public configuration types...
      return {/* ... */};
    });
    // test/config.test.ts
    import * as sut from '../src/config';
    
    // Within a test...
    const env = {/* ... */}; // Test environment.
    expect(config(env)).toEqual(/* ... */); // Expected config for the environment.

    Keywords

    none

    Install

    npm i atrace-settings

    DownloadsWeekly Downloads

    1

    Version

    0.8.4

    License

    MIT

    Unpacked Size

    39.3 kB

    Total Files

    6

    Last publish

    Collaborators

    • mtth