From eeeaae24aee216c1bfc2925d787080e5c79d20a4 Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Fri, 25 Oct 2024 01:03:17 +0200
Subject: [PATCH 1/6] feat: add initial seed parameter to constructors

---
 src/faker.ts               | 19 ++++++++-
 src/internal/seed.ts       |  8 ++++
 src/simple-faker.ts        | 27 +++++++++++--
 src/utils/mersenne.ts      | 17 ++++++--
 test/faker.spec.ts         | 81 ++++++++++++++++++++++++++++----------
 test/internal/seed.spec.ts | 11 ++++++
 test/simple-faker.spec.ts  | 54 ++++++++++++++++++++++++-
 7 files changed, 187 insertions(+), 30 deletions(-)
 create mode 100644 src/internal/seed.ts
 create mode 100644 test/internal/seed.spec.ts

diff --git a/src/faker.ts b/src/faker.ts
index 77630d29ee7..a70d29e7472 100644
--- a/src/faker.ts
+++ b/src/faker.ts
@@ -125,6 +125,11 @@ export class Faker extends SimpleFaker {
    * 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.
    * Defaults to faker's Mersenne Twister based pseudo random number generator.
+   * @param options.seed The initial seed to use.
+   * The seed can be used to generate reproducible values.
+   * Refer to the `seed()` method for more information.
+   * This option is ignored if `randomizer` is specified.
+   * Defaults to a random seed.
    *
    * @example
    * import { Faker, es } from '@faker-js/faker';
@@ -157,8 +162,20 @@ export class Faker extends SimpleFaker {
      * @default generateMersenne53Randomizer()
      */
     randomizer?: Randomizer;
+
+    /**
+     * The initial seed to use.
+     * The seed can be used to generate reproducible values.
+     *
+     * Refer to the `seed()` method for more information.
+     *
+     * This option is ignored if `randomizer` is specified.
+     *
+     * @default randomSeed()
+     */
+    seed?: number;
   }) {
-    super({ randomizer: options.randomizer });
+    super({ seed: options.seed, randomizer: options.randomizer });
 
     let { locale } = options;
 
diff --git a/src/internal/seed.ts b/src/internal/seed.ts
new file mode 100644
index 00000000000..3ff484b2768
--- /dev/null
+++ b/src/internal/seed.ts
@@ -0,0 +1,8 @@
+/**
+ * Generates a random seed.
+ *
+ * @internal
+ */
+export function randomSeed(): number {
+  return Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER);
+}
diff --git a/src/simple-faker.ts b/src/simple-faker.ts
index 743df923570..79faf05c942 100644
--- a/src/simple-faker.ts
+++ b/src/simple-faker.ts
@@ -1,3 +1,4 @@
+import { randomSeed } from './internal/seed';
 import { DatatypeModule } from './modules/datatype';
 import { SimpleDateModule } from './modules/date';
 import { SimpleHelpersModule } from './modules/helpers';
@@ -97,6 +98,11 @@ export class SimpleFaker {
    * 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.
    * Defaults to faker's Mersenne Twister based pseudo random number generator.
+   * @param options.seed The initial seed to use.
+   * The seed can be used to generate reproducible values.
+   * Refer to the `seed()` method for more information.
+   * This option is ignored if `randomizer` is specified.
+   * Defaults to a random seed.
    *
    * @example
    * import { SimpleFaker } from '@faker-js/faker';
@@ -120,9 +126,24 @@ export class SimpleFaker {
        * @default generateMersenne53Randomizer()
        */
       randomizer?: Randomizer;
+
+      /**
+       * The initial seed to use.
+       * The seed can be used to generate reproducible values.
+       *
+       * Refer to the `seed()` method for more information.
+       *
+       * This option is ignored if `randomizer` is specified.
+       *
+       * @default randomSeed()
+       */
+      seed?: number;
     } = {}
   ) {
-    const { randomizer = generateMersenne53Randomizer() } = options;
+    const {
+      seed = randomSeed(),
+      randomizer = generateMersenne53Randomizer(seed),
+    } = options;
 
     this._randomizer = randomizer;
   }
@@ -247,9 +268,7 @@ export class SimpleFaker {
    * @since 6.0.0
    */
   seed(seed?: number | number[]): number | number[];
-  seed(
-    seed: number | number[] = Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER)
-  ): number | number[] {
+  seed(seed: number | number[] = randomSeed()): number | number[] {
     this._randomizer.seed(seed);
 
     return seed;
diff --git a/src/utils/mersenne.ts b/src/utils/mersenne.ts
index de415f9166e..8aa525cf21a 100644
--- a/src/utils/mersenne.ts
+++ b/src/utils/mersenne.ts
@@ -1,14 +1,19 @@
 import { MersenneTwister19937 } from '../internal/mersenne';
+import { randomSeed } from '../internal/seed';
 import type { Randomizer } from '../randomizer';
 
 /**
  * Generates a MersenneTwister19937 randomizer with 32 bits of precision.
  * This is the default randomizer used by faker prior to v9.0.
+ *
+ * @param seed The initial seed to use. Defaults to a random number.
  */
-export function generateMersenne32Randomizer(): Randomizer {
+export function generateMersenne32Randomizer(
+  seed: number = randomSeed()
+): Randomizer {
   const twister = new MersenneTwister19937();
 
-  twister.initGenrand(Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER));
+  twister.initGenrand(seed);
 
   return {
     next(): number {
@@ -27,11 +32,15 @@ export function generateMersenne32Randomizer(): Randomizer {
 /**
  * Generates a MersenneTwister19937 randomizer with 53 bits of precision.
  * This is the default randomizer used by faker starting with v9.0.
+ *
+ * @param seed The initial seed to use. Defaults to a random number.
  */
-export function generateMersenne53Randomizer(): Randomizer {
+export function generateMersenne53Randomizer(
+  seed: number = randomSeed()
+): Randomizer {
   const twister = new MersenneTwister19937();
 
-  twister.initGenrand(Math.ceil(Math.random() * Number.MAX_SAFE_INTEGER));
+  twister.initGenrand(seed);
 
   return {
     next(): number {
diff --git a/test/faker.spec.ts b/test/faker.spec.ts
index 6d928d63652..78d4c5f82f6 100644
--- a/test/faker.spec.ts
+++ b/test/faker.spec.ts
@@ -1,18 +1,10 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { Faker, faker } from '../src';
+import { Faker, faker, generateMersenne53Randomizer } from '../src';
 import { FakerError } from '../src/errors/faker-error';
 import { keys } from '../src/internal/keys';
 
 describe('faker', () => {
-  it('should throw error if no locales passed', () => {
-    expect(() => new Faker({ locale: [] })).toThrow(
-      new FakerError(
-        'The locale option must contain at least one locale definition.'
-      )
-    );
-  });
-
   it('should not log anything on startup', async () => {
     const spies: MockInstance[] = keys(console)
       .filter((key) => typeof console[key] === 'function')
@@ -69,19 +61,68 @@ describe('faker', () => {
     });
   });
 
-  describe('randomizer', () => {
-    it('should be possible to provide a custom Randomizer', () => {
-      const customFaker = new Faker({
-        locale: {},
-        randomizer: {
-          next: () => 0,
-          seed: () => void 0,
-        },
+  describe('constructor()', () => {
+    describe('locale', () => {
+      it('should throw error if no locales passed', () => {
+        expect(() => new Faker({ locale: [] })).toThrow(
+          new FakerError(
+            'The locale option must contain at least one locale definition.'
+          )
+        );
+      });
+    });
+
+    describe('randomizer', () => {
+      it('should be possible to provide a custom Randomizer', () => {
+        const customFaker = new Faker({
+          locale: {},
+          randomizer: {
+            next: () => 0,
+            seed: () => void 0,
+          },
+        });
+
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
       });
+    });
+
+    describe('seed', () => {
+      it('should be possible to provide an initial seed', () => {
+        const customFaker = new Faker({
+          locale: {},
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
 
-      expect(customFaker.number.int()).toBe(0);
-      expect(customFaker.number.int()).toBe(0);
-      expect(customFaker.number.int()).toBe(0);
+        customFaker.seed(12345);
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+      });
+
+      it('should prioritize the randomizer over the seed', () => {
+        const customFaker = new Faker({
+          locale: {},
+          randomizer: generateMersenne53Randomizer(67890),
+          seed: 12345, // This seed should be ignored
+        });
+
+        expect(customFaker.number.int()).toBe(3319821087749105);
+        expect(customFaker.number.int()).toBe(8108180265059478);
+        expect(customFaker.number.int()).toBe(1714153343835993);
+
+        customFaker.seed(67890);
+
+        expect(customFaker.number.int()).toBe(3319821087749105);
+        expect(customFaker.number.int()).toBe(8108180265059478);
+        expect(customFaker.number.int()).toBe(1714153343835993);
+      });
     });
   });
 
diff --git a/test/internal/seed.spec.ts b/test/internal/seed.spec.ts
new file mode 100644
index 00000000000..c3503524c8d
--- /dev/null
+++ b/test/internal/seed.spec.ts
@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest';
+import { randomSeed } from '../../src/internal/seed';
+
+describe('seed', () => {
+  it('should generate a random seed', () => {
+    const actual = randomSeed();
+
+    expect(actual).toBeTypeOf('number');
+    expect(actual).not.toBe(randomSeed());
+  });
+});
diff --git a/test/simple-faker.spec.ts b/test/simple-faker.spec.ts
index aa6f00c1892..9bbfad30d99 100644
--- a/test/simple-faker.spec.ts
+++ b/test/simple-faker.spec.ts
@@ -1,6 +1,6 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { SimpleFaker, simpleFaker } from '../src';
+import { generateMersenne53Randomizer, SimpleFaker, simpleFaker } from '../src';
 import { keys } from '../src/internal/keys';
 
 describe('simpleFaker', () => {
@@ -20,6 +20,58 @@ describe('simpleFaker', () => {
     }
   });
 
+  describe('constructor()', () => {
+    describe('randomizer', () => {
+      it('should be possible to provide a custom Randomizer', () => {
+        const customFaker = new SimpleFaker({
+          randomizer: {
+            next: () => 0,
+            seed: () => void 0,
+          },
+        });
+
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+        expect(customFaker.number.int()).toBe(0);
+      });
+    });
+
+    describe('seed', () => {
+      it('should be possible to provide an initial seed', () => {
+        const customFaker = new SimpleFaker({
+          seed: 12345,
+        });
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+
+        customFaker.seed(12345); // Retry with the expected seed
+
+        expect(customFaker.number.int()).toBe(8373237378417847);
+        expect(customFaker.number.int()).toBe(2849657659447330);
+        expect(customFaker.number.int()).toBe(1656593383470774);
+      });
+
+      it('should prioritize the randomizer over the seed', () => {
+        const customFaker = new SimpleFaker({
+          randomizer: generateMersenne53Randomizer(67890),
+          seed: 12345, // This seed should be ignored
+        });
+
+        expect(customFaker.number.int()).toBe(3319821087749105);
+        expect(customFaker.number.int()).toBe(8108180265059478);
+        expect(customFaker.number.int()).toBe(1714153343835993);
+
+        customFaker.seed(67890); // Retry with the expected seed
+
+        expect(customFaker.number.int()).toBe(3319821087749105);
+        expect(customFaker.number.int()).toBe(8108180265059478);
+        expect(customFaker.number.int()).toBe(1714153343835993);
+      });
+    });
+  });
+
   // This is only here for coverage
   // The actual test is in mersenne.spec.ts
   describe('seed()', () => {

From f9d09576d3208d8c41eb2e3c5c4b0affbed0d861 Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Sat, 26 Oct 2024 02:28:02 +0200
Subject: [PATCH 2/6] chore: apply suggestions

---
 src/faker.ts        | 3 ---
 src/simple-faker.ts | 9 ++++++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/faker.ts b/src/faker.ts
index a70d29e7472..d3b60e7b2ac 100644
--- a/src/faker.ts
+++ b/src/faker.ts
@@ -128,7 +128,6 @@ export class Faker extends SimpleFaker {
    * @param options.seed The initial seed to use.
    * The seed can be used to generate reproducible values.
    * Refer to the `seed()` method for more information.
-   * This option is ignored if `randomizer` is specified.
    * Defaults to a random seed.
    *
    * @example
@@ -169,8 +168,6 @@ export class Faker extends SimpleFaker {
      *
      * Refer to the `seed()` method for more information.
      *
-     * This option is ignored if `randomizer` is specified.
-     *
      * @default randomSeed()
      */
     seed?: number;
diff --git a/src/simple-faker.ts b/src/simple-faker.ts
index 79faf05c942..b74a4465241 100644
--- a/src/simple-faker.ts
+++ b/src/simple-faker.ts
@@ -101,7 +101,6 @@ export class SimpleFaker {
    * @param options.seed The initial seed to use.
    * The seed can be used to generate reproducible values.
    * Refer to the `seed()` method for more information.
-   * This option is ignored if `randomizer` is specified.
    * Defaults to a random seed.
    *
    * @example
@@ -133,18 +132,22 @@ export class SimpleFaker {
        *
        * Refer to the `seed()` method for more information.
        *
-       * This option is ignored if `randomizer` is specified.
-       *
        * @default randomSeed()
        */
       seed?: number;
     } = {}
   ) {
     const {
+      seed: originalSeed,
       seed = randomSeed(),
+      randomizer: originalRandomizer,
       randomizer = generateMersenne53Randomizer(seed),
     } = options;
 
+    if (originalRandomizer != null && originalSeed != null) {
+      randomizer.seed(seed);
+    }
+
     this._randomizer = randomizer;
   }
 

From d1a313c27c615c6e4e946698f130c398f330d1dc Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Sat, 26 Oct 2024 02:32:31 +0200
Subject: [PATCH 3/6] chore: simplify

---
 src/simple-faker.ts | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/src/simple-faker.ts b/src/simple-faker.ts
index b74a4465241..b7ddcc578e3 100644
--- a/src/simple-faker.ts
+++ b/src/simple-faker.ts
@@ -137,18 +137,13 @@ export class SimpleFaker {
       seed?: number;
     } = {}
   ) {
-    const {
-      seed: originalSeed,
-      seed = randomSeed(),
-      randomizer: originalRandomizer,
-      randomizer = generateMersenne53Randomizer(seed),
-    } = options;
+    const { seed, randomizer } = options;
 
-    if (originalRandomizer != null && originalSeed != null) {
+    if (seed != null && randomizer != null) {
       randomizer.seed(seed);
     }
 
-    this._randomizer = randomizer;
+    this._randomizer = randomizer ?? generateMersenne53Randomizer(seed);
   }
 
   /**

From 3d6c42eb71652ae2e5f7076d0aac15d48522dd5b Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Sat, 26 Oct 2024 02:34:46 +0200
Subject: [PATCH 4/6] chore: sort

---
 src/faker.ts        | 2 +-
 src/simple-faker.ts | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/faker.ts b/src/faker.ts
index d3b60e7b2ac..a360a59b1c8 100644
--- a/src/faker.ts
+++ b/src/faker.ts
@@ -172,7 +172,7 @@ export class Faker extends SimpleFaker {
      */
     seed?: number;
   }) {
-    super({ seed: options.seed, randomizer: options.randomizer });
+    super({ randomizer: options.randomizer, seed: options.seed });
 
     let { locale } = options;
 
diff --git a/src/simple-faker.ts b/src/simple-faker.ts
index b7ddcc578e3..fd89f6c0bca 100644
--- a/src/simple-faker.ts
+++ b/src/simple-faker.ts
@@ -137,9 +137,9 @@ export class SimpleFaker {
       seed?: number;
     } = {}
   ) {
-    const { seed, randomizer } = options;
+    const { randomizer, seed } = options;
 
-    if (seed != null && randomizer != null) {
+    if (randomizer != null && seed != null) {
       randomizer.seed(seed);
     }
 

From b77af40411cee001ac39d2fed062fdf7bd6cf79d Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Sat, 26 Oct 2024 02:45:14 +0200
Subject: [PATCH 5/6] chore: fix tests

---
 test/faker.spec.ts        | 24 +++++++++++++-----------
 test/simple-faker.spec.ts | 24 +++++++++++++-----------
 2 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/test/faker.spec.ts b/test/faker.spec.ts
index 78d4c5f82f6..dba19421912 100644
--- a/test/faker.spec.ts
+++ b/test/faker.spec.ts
@@ -1,6 +1,6 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { Faker, faker, generateMersenne53Randomizer } from '../src';
+import { Faker, faker, generateMersenne32Randomizer } from '../src';
 import { FakerError } from '../src/errors/faker-error';
 import { keys } from '../src/internal/keys';
 
@@ -105,23 +105,25 @@ describe('faker', () => {
         expect(customFaker.number.int()).toBe(2849657659447330);
         expect(customFaker.number.int()).toBe(1656593383470774);
       });
+    });
 
-      it('should prioritize the randomizer over the seed', () => {
+    describe('randomizer+seed', () => {
+      it('should take apply both the randomizer and seed', () => {
         const customFaker = new Faker({
           locale: {},
-          randomizer: generateMersenne53Randomizer(67890),
-          seed: 12345, // This seed should be ignored
+          randomizer: generateMersenne32Randomizer(67890),
+          seed: 12345,
         });
 
-        expect(customFaker.number.int()).toBe(3319821087749105);
-        expect(customFaker.number.int()).toBe(8108180265059478);
-        expect(customFaker.number.int()).toBe(1714153343835993);
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
 
-        customFaker.seed(67890);
+        customFaker.seed(12345); // Retry with the expected seed
 
-        expect(customFaker.number.int()).toBe(3319821087749105);
-        expect(customFaker.number.int()).toBe(8108180265059478);
-        expect(customFaker.number.int()).toBe(1714153343835993);
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
       });
     });
   });
diff --git a/test/simple-faker.spec.ts b/test/simple-faker.spec.ts
index 9bbfad30d99..02c860a50ee 100644
--- a/test/simple-faker.spec.ts
+++ b/test/simple-faker.spec.ts
@@ -1,6 +1,6 @@
 import type { MockInstance } from 'vitest';
 import { describe, expect, it, vi } from 'vitest';
-import { generateMersenne53Randomizer, SimpleFaker, simpleFaker } from '../src';
+import { generateMersenne32Randomizer, SimpleFaker, simpleFaker } from '../src';
 import { keys } from '../src/internal/keys';
 
 describe('simpleFaker', () => {
@@ -52,22 +52,24 @@ describe('simpleFaker', () => {
         expect(customFaker.number.int()).toBe(2849657659447330);
         expect(customFaker.number.int()).toBe(1656593383470774);
       });
+    });
 
-      it('should prioritize the randomizer over the seed', () => {
+    describe('randomizer+seed', () => {
+      it('should take apply both the randomizer and seed', () => {
         const customFaker = new SimpleFaker({
-          randomizer: generateMersenne53Randomizer(67890),
-          seed: 12345, // This seed should be ignored
+          randomizer: generateMersenne32Randomizer(67890),
+          seed: 12345,
         });
 
-        expect(customFaker.number.int()).toBe(3319821087749105);
-        expect(customFaker.number.int()).toBe(8108180265059478);
-        expect(customFaker.number.int()).toBe(1714153343835993);
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
 
-        customFaker.seed(67890); // Retry with the expected seed
+        customFaker.seed(12345); // Retry with the expected seed
 
-        expect(customFaker.number.int()).toBe(3319821087749105);
-        expect(customFaker.number.int()).toBe(8108180265059478);
-        expect(customFaker.number.int()).toBe(1714153343835993);
+        expect(customFaker.number.int()).toBe(8373237322874880);
+        expect(customFaker.number.int()).toBe(8017800868134912);
+        expect(customFaker.number.int()).toBe(2849657711493120);
       });
     });
   });

From 604e144d6301d0f96a7a1aa28a79b57241f8034f Mon Sep 17 00:00:00 2001
From: ST-DDT <ST-DDT@gmx.de>
Date: Sat, 26 Oct 2024 18:01:15 +0200
Subject: [PATCH 6/6] chore: apply suggestions

---
 src/faker.ts        | 2 +-
 src/simple-faker.ts | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/faker.ts b/src/faker.ts
index a360a59b1c8..0b03788b3be 100644
--- a/src/faker.ts
+++ b/src/faker.ts
@@ -168,7 +168,7 @@ export class Faker extends SimpleFaker {
      *
      * Refer to the `seed()` method for more information.
      *
-     * @default randomSeed()
+     * Defaults to a random seed.
      */
     seed?: number;
   }) {
diff --git a/src/simple-faker.ts b/src/simple-faker.ts
index fd89f6c0bca..1371e68a773 100644
--- a/src/simple-faker.ts
+++ b/src/simple-faker.ts
@@ -132,7 +132,7 @@ export class SimpleFaker {
        *
        * Refer to the `seed()` method for more information.
        *
-       * @default randomSeed()
+       * Defaults to a random seed.
        */
       seed?: number;
     } = {}