feat: introduce FakerCore

src/config.ts

@@ -0,0 +1,20 @@
+/**
+ * The possible configuration options, that can be set.
+ * This type exists to be extended for plugins via type augmentation.
+ *
+ * The `@default` tag is used to indicate the default value, that should be used if, the config is absent.
+ */
+export interface FakerConfig {
+  /**
+   * The function used to generate the `refDate` date instance, if not provided as method param.
+   * The function must return a new valid `Date` instance for every call.
+   *
+   * @see [Reproducible Results](https://fakerjs.dev/guide/usage.html#reproducible-results)
+   * @see faker.seed(): For generating reproducible values.
+   *
+   * @since 9.0.0
+   *
+   * @default () => new Date()
+   */
+  refDate?: () => Date;
+}

src/core.ts

@@ -0,0 +1,25 @@
+import type { FakerConfig } from './config';
+import type { LocaleDefinition } from './definitions';
+import type { Randomizer } from './randomizer';
+
+/**
+ * The core grants access to the locale data, the randomizer and config settings.
+ */
+export interface FakerCore {
+  /**
+   * The locale data associated with this instance.
+   *
+   * Always present, but it might be empty if the locale data is not available.
+   */
+  readonly locale: LocaleDefinition;
+
+  /**
+   * The randomizer used to generate random values.
+   */
+  readonly randomizer: Randomizer;
+
+  /**
+   * The configuration settings used by this instance.
+   */
+  readonly config: FakerConfig;
+}

src/faker.ts

@@ -1,6 +1,8 @@
+import type { FakerCore } from './core';
 import type { LocaleDefinition, MetadataDefinition } from './definitions';
 import { FakerError } from './errors/faker-error';
 import { deprecated } from './internal/deprecated';
+import { generateMersenne53Randomizer } from './internal/mersenne';
 import type { LocaleProxy } from './locale-proxy';
 import { createLocaleProxy } from './locale-proxy';
 import { AirlineModule } from './modules/airline';
@@ -58,7 +60,6 @@ import { mergeLocales } from './utils/merge-locales';
  * customFaker.music.genre(); // throws Error as this data is not available in `es`
  */
 export class Faker extends SimpleFaker {
-  readonly rawDefinitions: LocaleDefinition;
   readonly definitions: LocaleProxy;
 
   readonly airline: AirlineModule = new AirlineModule(this);
@@ -85,6 +86,10 @@ export class Faker extends SimpleFaker {
   readonly vehicle: VehicleModule = new VehicleModule(this);
   readonly word: WordModule = new WordModule(this);
 
+  get rawDefinitions(): LocaleDefinition {
+    return this.fakerCore.locale;
+  }
+
   // Aliases
   /** @deprecated Use {@link Faker#location} instead */
   get address(): AddressModule {
@@ -138,27 +143,40 @@ export class Faker extends SimpleFaker {
    *
    * @since 8.0.0
    */
-  constructor(options: {
-    /**
-     * The locale data to use for this instance.
-     * If an array is provided, the first locale that has a definition for a given property will be used.
-     *
-     * @see mergeLocales(): For more information about how the locales are merged.
-     */
-    locale: LocaleDefinition | LocaleDefinition[];
+  constructor(
+    options:
+      | {
+          /**
+           * The locale data to use for this instance.
+           * If an array is provided, the first locale that has a definition for a given property will be used.
+           *
+           * @see mergeLocales(): For more information about how the locales are merged.
+           */
+          locale: LocaleDefinition | LocaleDefinition[];
 
-    /**
-     * The Randomizer to use.
-     * Specify this only if you want to use it to achieve a specific goal,
-     * such as sharing the same random generator with other instances/tools.
-     *
-     * @default generateMersenne53Randomizer()
-     */
+          /**
+           * The Randomizer to use.
+           * Specify this only if you want to use it to achieve a specific goal,
+           * such as sharing the same random generator with other instances/tools.
+           *
+           * @default generateMersenne53Randomizer()
+           */
+          randomizer?: Randomizer;
+        }
+      | {
+          /**
+           * The faker core with the randomizer, locale data and config to use.
+           */
+          fakerCore: FakerCore;
+        }
+  );
+  constructor(options: {
+    locale?: LocaleDefinition | LocaleDefinition[];
     randomizer?: Randomizer;
+    fakerCore?: FakerCore;
   }) {
-    super({ randomizer: options.randomizer });
-
-    let { locale } = options;
+    const { randomizer = generateMersenne53Randomizer(), fakerCore } = options;
+    let { locale = {} } = options;
 
     if (Array.isArray(locale)) {
       if (locale.length === 0) {
@@ -170,7 +188,8 @@ export class Faker extends SimpleFaker {
       locale = mergeLocales(locale);
     }
 
-    this.rawDefinitions = locale;
+    super({ fakerCore: fakerCore ?? { locale, randomizer, config: {} } });
+
     this.definitions = createLocaleProxy(this.rawDefinitions);
   }
 
@@ -186,7 +205,7 @@ export class Faker extends SimpleFaker {
    * @since 8.1.0
    */
   getMetadata(): MetadataDefinition {
-    return this.rawDefinitions.metadata ?? {};
+    return this.fakerCore.locale.metadata ?? {};
   }
 }
 

src/modules/number/index.ts

@@ -96,8 +96,7 @@ export class NumberModule extends SimpleModuleBase {
       throw new FakerError(`Max ${max} should be greater than min ${min}.`);
     }
 
-    // @ts-expect-error: access private member field
-    const randomizer = this.faker._randomizer;
+    const { randomizer } = this.faker.fakerCore;
     const real = randomizer.next();
     const delta = effectiveMax - effectiveMin + 1; // +1 for inclusive max bounds and even distribution
     return Math.floor(real * delta + effectiveMin) * multipleOf;
@@ -214,8 +213,7 @@ export class NumberModule extends SimpleModuleBase {
       return int / factor;
     }
 
-    // @ts-expect-error: access private member field
-    const randomizer = this.faker._randomizer;
+    const { randomizer } = this.faker.fakerCore;
     const real = randomizer.next();
     return real * (max - min) + min;
   }

src/simple-faker.ts

@@ -1,3 +1,4 @@
+import type { FakerCore } from './core';
 import { generateMersenne53Randomizer } from './internal/mersenne';
 import { DatatypeModule } from './modules/datatype';
 import { SimpleDateModule } from './modules/date';
@@ -26,13 +27,13 @@ import type { Randomizer } from './randomizer';
  * simpleFaker.string.uuid(); // 'c50e1f5c-86e8-4aa9-888e-168e0a182519'
  */
 export class SimpleFaker {
-  protected _defaultRefDate: () => Date = () => new Date();
+  readonly fakerCore: FakerCore;
 
   /**
    * Gets a new reference date used to generate relative dates.
    */
   get defaultRefDate(): () => Date {
-    return this._defaultRefDate;
+    return this.fakerCore.config.refDate ?? (() => new Date());
   }
 
   /**
@@ -72,15 +73,12 @@ export class SimpleFaker {
     dateOrSource: string | Date | number | (() => Date) = () => new Date()
   ): void {
     if (typeof dateOrSource === 'function') {
-      this._defaultRefDate = dateOrSource;
+      this.fakerCore.config.refDate = dateOrSource;
     } else {
-      this._defaultRefDate = () => new Date(dateOrSource);
+      this.fakerCore.config.refDate = () => new Date(dateOrSource);
     }
   }
 
-  /** @internal */
-  private readonly _randomizer: Randomizer;
-
   readonly datatype: DatatypeModule = new DatatypeModule(this);
   readonly date: SimpleDateModule = new SimpleDateModule(this);
   readonly helpers: SimpleHelpersModule = new SimpleHelpersModule(this);
@@ -110,21 +108,37 @@ export class SimpleFaker {
    *
    * @since 8.1.0
    */
+  constructor(
+    options?:
+      | {
+          /**
+           * The Randomizer to use.
+           * Specify this only if you want to use it to achieve a specific goal,
+           * such as sharing the same random generator with other instances/tools.
+           *
+           * @default generateMersenne53Randomizer()
+           */
+          randomizer?: Randomizer;
+        }
+      | {
+          /**
+           * The faker core with the randomizer and config to use.
+           */
+          fakerCore: FakerCore;
+        }
+  );
   constructor(
     options: {
-      /**
-       * The Randomizer to use.
-       * Specify this only if you want to use it to achieve a specific goal,
-       * such as sharing the same random generator with other instances/tools.
-       *
-       * @default generateMersenne53Randomizer()
-       */
       randomizer?: Randomizer;
+      fakerCore?: FakerCore;
     } = {}
   ) {
-    const { randomizer = generateMersenne53Randomizer() } = options;
+    const {
+      randomizer = generateMersenne53Randomizer(),
+      fakerCore = { locale: {}, randomizer, config: {} },
+    } = options;
 
-    this._randomizer = randomizer;
+    this.fakerCore = fakerCore;
   }
 
   /**
@@ -250,7 +264,7 @@ export class SimpleFaker {
   seed(
     seed: number | number[] = Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER)
   ): number | number[] {
-    this._randomizer.seed(seed);
+    this.fakerCore.randomizer.seed(seed);
 
     return seed;
   }

test/all-functional.spec.ts

@@ -3,13 +3,7 @@ import type { Faker, allLocales } from '../src';
 import { allFakers, fakerEN } from '../src';
 import { keys } from '../src/internal/keys';
 
-const IGNORED_MODULES = new Set([
-  'rawDefinitions',
-  'definitions',
-  'helpers',
-  '_randomizer',
-  '_defaultRefDate',
-]);
+const IGNORED_MODULES = new Set(['rawDefinitions', 'helpers', 'fakerCore']);
 
 function getMethodNamesByModules(faker: Faker): { [module: string]: string[] } {
   return Object.fromEntries(

test/modules/number.spec.ts

@@ -629,8 +629,7 @@ describe('number', () => {
 
   describe('value range tests', () => {
     const customFaker = new SimpleFaker();
-    // @ts-expect-error: access private member field
-    const randomizer = customFaker._randomizer;
+    const { randomizer } = customFaker.fakerCore;
     describe('int', () => {
       it('should be able to return 0', () => {
         randomizer.next = () => 0;