Implement Fraction JSON serialization and deserialization

src/__tests__/fraction.spec.ts

@@ -725,3 +725,43 @@ describe('Fraction', () => {
     );
   });
 });
+
+describe('JSON serialization', () => {
+  it('can serialize an array of fractions along with other data', () => {
+    const serialized = JSON.stringify([
+      new Fraction(42),
+      2,
+      new Fraction(-5, 3),
+      new Fraction('1.234'),
+      'hello',
+      new Fraction({s: 0, n: 0, d: 1}),
+    ]);
+
+    expect(serialized).toBe(
+      '[{"n":42,"d":1},2,{"n":-5,"d":3},{"n":617,"d":500},"hello",{"n":0,"d":1}]'
+    );
+  });
+
+  it('can revive an array of fractions along with other data', () => {
+    const serialized =
+      '[{"n":42,"d":1},2,{"n":-5,"d":3},{"n":617,"d":500},"hello",{"n":0,"d":1}]';
+    const data = JSON.parse(serialized, Fraction.reviver);
+    expect(data).toHaveLength(6);
+
+    expect(data[0]).toBeInstanceOf(Fraction);
+    expect(data[0]).toEqual({s: 1, n: 42, d: 1});
+
+    expect(data[1]).toBe(2);
+
+    expect(data[2]).toBeInstanceOf(Fraction);
+    expect(data[2]).toEqual({s: -1, n: 5, d: 3});
+
+    expect(data[3]).toBeInstanceOf(Fraction);
+    expect(data[3].equals('1.234')).toBe(true);
+
+    expect(data[4]).toBe('hello');
+
+    expect(data[5]).toBeInstanceOf(Fraction);
+    expect(data[5]).toEqual({s: 0, n: 0, d: 1});
+  });
+});

src/fraction.ts

@@ -361,6 +361,44 @@ export class Fraction {
     return result + decimals + '...';
   }
 
+  /**
+   * Serialize the fraction to a JSON compatible object.
+   * @returns An object with properties 'n', and 'd' corresponding to a signed numerator and an unsigned denominator respectively.
+   */
+  toJSON(): UnsignedFraction {
+    return {
+      n: this.n * this.s,
+      d: this.d,
+    };
+  }
+
+  /**
+   * Revive a {@link Fraction} instance produced by Fraction.toJSON(). Return everything else as is.
+   *
+   * Intended usage:
+   * ```ts
+   * const data = JSON.parse(serializedData, Fraction.reviver);
+   * ```
+   *
+   * @param key Property name.
+   * @param value Property value.
+   * @returns Deserialized {@link Fraction} instance or other data without modifications.
+   * @throws An error if the numerator or denominator exceeds `Number.MAX_SAFE_INTEGER`.
+   */
+  static reviver(key: string, value: any) {
+    if (
+      typeof value === 'object' &&
+      'n' in value &&
+      Number.isInteger(value.n) &&
+      'd' in value &&
+      Number.isInteger(value.d) &&
+      Object.keys(value).length === 2
+    ) {
+      return new Fraction(value as UnsignedFraction);
+    }
+    return value;
+  }
+
   /**
    * Returns an array of continued fraction elements.
    *