TheAlgorithms · sibalonecoding-code · Mar 2, 2026
@@ -1,48 +1,63 @@
-/*
- * Even Number: https://simple.wikipedia.org/wiki/Even_number
+/**
+ * @license             GPL-3.0 or later
  *
- * function to check if number is even
- * return true if number is even
- * else false
+ * @description         Checking if number is even
  */
 
 /**
- * @function isEven
- * @description - Checking if number is even using divisibility by 2
+ * @function            isEven
+ * @description         Checking if number is even
+ *
+ * If the division: number / 2 results in remainder being 0
+ * the number is even, otherwise it's odd
  *
- * If number is divisible by 2 i.e remainder = 0, then it is even
- * therefore, the function will return true
+ * @param {number}      number - Value to check
+ * @return {boolean}    True if number is even else False
  *
- * If number is not divisible by 2 i.e remainder != 0, then it is not even i.e odd
- * therefore, the function will return false
- * @param {number} number
- * @return {boolean}
+ * @see https://simple.wikipedia.org/wiki/Even_number to get
+ * more details on even numbers
  */
-export const isEven = (number) => number % 2 === 0
+const isEven = (number) => {
+  if (typeof number !== 'number' || Number.isNaN(number))
+    throw new TypeError('Argument is Not a Number')
+
+  return Boolean(number % 2) === false
+}
 
 /**
- * @function isEvenBitwise
- * @description - Checking if number is even using bitwise operator
- * Bitwise AND (&) compares the bits of the 32
- * bit binary representations of the number and
- * returns a number after comparing each bit:
+ * @function            isEvenBitwise
+ * @description         Checking if number is even using bitwise
+ *                      operation
  *
- * 0 & 0 -> 0
- * 0 & 1 -> 0
- * 1 & 0 -> 0
- * 1 & 1 -> 1
+ * Bitwise AND (&) compares the bits of the 32 bit binary
+ * representations of the number and returns a number after
+ * comparing each bit:
+ *  0 & 0 -> 0
+ *  0 & 1 -> 0
+ *  1 & 0 -> 0
+ *  1 & 1 -> 1
+ * For odd numbers, the LSB (Least Significant Bit) will be 1
+ * and for even numbers, the LSB will be 0. As the number is
+ * compared to one, all other bits will become 0
+ *  0 1 1 1 = 7
+ *  & & & &
+ *  0 0 0 1 = 1
+ *  ↓ ↓ ↓ ↓
+ *  0 0 0 1 = odd since LSB is equal to 1
  *
- * For odd numbers, the last binary bit will be 1
- * and for even numbers, the last binary bit will
- * be 0.
+ * @param {number}      number - Value to check
+ * @return {boolean}    True if number is even else False
  *
- * As the number is compared with one, all the
- * other bits except the last will become 0. The
- * last bit will be 0 for even numbers and 1 for
- * odd numbers, which is checked with the use
- * of the equality operator.
- * @param {number} number
- * @returns {boolean}
- * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_AND
+ * @see https://en.wikipedia.org/wiki/Bit_numbering to get
+ * details on LSB (Least Significant Bit) and
+ * https://en.wikipedia.org/wiki/Bitwise_operation#AND
+ * to get details on bitwise AND operator
  */
-export const isEvenBitwise = (number) => (number & 1) === 0
+const isEvenBitwise = (number) => {
+  if (typeof number !== 'number' || Number.isNaN(number))
+    throw new TypeError('Argument is Not a Number')
+
+  return Boolean(number & 1) === false
+}
+
+export { isEven, isEvenBitwise }
@@ -1,25 +1,51 @@
 import { isEven, isEvenBitwise } from '../IsEven'
 
 describe('Testing isEven function', () => {
-  it('should return if the number is even or not', () => {
+  const randomNumber = Math.floor(Math.random() * 1999999) - 999999
+
+  it('will test a value which should be even: 4', () => {
     const isEvenNumber = isEven(4)
     expect(isEvenNumber).toBe(true)
   })
 
-  it('should return if the number is even or not', () => {
+  it("will test a value which shouldn't be even: 7", () => {
     const isEvenNumber = isEven(7)
     expect(isEvenNumber).toBe(false)
   })
+
+  it(`will test a random value: ${randomNumber}`, () => {
+    const isEvenNumber = isEven(randomNumber)
+    expect(isEvenNumber).toBe(Boolean(randomNumber % 2) === false)
+  })
+
+  it('will test a TypeError for non-number inputs', () => {
+    expect(() => isEven('10')).toThrow(TypeError)
+    expect(() => isEven(null)).toThrow(TypeError)
+    expect(() => isEven(undefined)).toThrow(TypeError)
+    expect(() => isEven(NaN)).toThrow(TypeError)
+  })
 })
 
 describe('Testing isEvenBitwise function', () => {
-  it('should return if the number is even or not', () => {
+  const randomNumber = Math.floor(Math.random() * 1999999) - 999999
+
+  it('will test a value which should be even: 6', () => {
     const isEvenNumber = isEvenBitwise(6)
     expect(isEvenNumber).toBe(true)
   })
 
-  it('should return if the number is even or not', () => {
+  it("will test a value which shouldn't be even: 3", () => {
     const isEvenNumber = isEvenBitwise(3)
     expect(isEvenNumber).toBe(false)
   })
+
+  it(`will test a random value: ${randomNumber}`, () => {
+    const isEvenNumber = isEvenBitwise(randomNumber)
+    expect(isEvenNumber).toBe(Boolean(randomNumber & 1) === false)
+  })
+
+  it('will test a TypeError for non-number inputs', () => {
+    expect(() => isEvenBitwise('10')).toThrow(TypeError)
+    expect(() => isEvenBitwise({})).toThrow(TypeError)
+  })
 })