feat: digits iterable supports negative numbers

src/core/DigitsIterable.js

@@ -1,9 +1,15 @@
 export class DigitsIterable {
   constructor(number) {
     if (typeof number === 'bigint' || number > Number.MAX_SAFE_INTEGER) {
-      this.number = BigInt(number);
+      this.number = number >= 0n ? BigInt(number) : BigInt(number) * -1n;
     } else {
-      this.number = number;
+      const integerPart = Math.trunc(number);
+      const fractionalPart = number - integerPart;
+
+      if (fractionalPart !== 0) {
+        throw new RangeError(`The number ${number} cannot be converted to an Iterable because it is not an integer`);
+      }
+      this.number = Math.abs(number);
     }
   }
 

src/core/__tests__/DigitsIterable.spec.js

@@ -47,4 +47,22 @@ describe('DigitsIterable', () => {
       0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
     ]);
   });
+
+  it('should work with negative integers', () => {
+    const digits = new DigitsIterable(-123);
+    const result = [...digits];
+    expect(result).toEqual([3, 2, 1]);
+  });
+
+  it('should work with negative Bigint', () => {
+    const digits = new DigitsIterable(BigInt(-123n));
+    const result = [...digits];
+    expect(result).toEqual([3, 2, 1]);
+  });
+
+  it('shouldn\'t work with decimal integers', () => {
+    const digitsIter = () => new DigitsIterable(123.45);
+    expect(digitsIter).toThrow(RangeError);
+    expect(digitsIter).toThrow('The number 123.45 cannot be converted to an Iterable because it is not an integer');
+  });
 });