feat: add decimal to hexadecimal conversion

Conversions/DecimalToHexadecimal.js

@@ -0,0 +1,28 @@
+/**
+ * @function decimalToHexadecimal
+ * @description Converts a decimal number (base-10) to its hexadecimal
+ *   (base-16) string representation without using JavaScript's
+ *   built-in toString(16).
+ * @param {number} decimal - A non-negative integer
+ * @returns {string} - The hexadecimal string representation in uppercase
+ * @see https://en.wikipedia.org/wiki/Hexadecimal
+ * @example decimalToHexadecimal(255) => "FF"
+ * @example decimalToHexadecimal(16) => "10"
+ * @example decimalToHexadecimal(0) => "0"
+ */
+const decimalToHexadecimal = (decimal) => {
+  if (!Number.isInteger(decimal) || decimal < 0) {
+    throw new TypeError('Input must be a non-negative integer')
+  }
+  if (decimal === 0) return '0'
+  const hexChars = '0123456789ABCDEF'
+  let hex = ''
+  let num = decimal
+  while (num > 0) {
+    hex = hexChars[num % 16] + hex
+    num = Math.floor(num / 16)
+  }
+  return hex
+}
+
+export { decimalToHexadecimal }

Conversions/test/DecimalToHexadecimal.test.js

@@ -0,0 +1,43 @@
+import { decimalToHexadecimal } from '../DecimalToHexadecimal.js'
+
+describe('decimalToHexadecimal', () => {
+  test("decimalToHexadecimal(0) returns '0'", () => {
+    expect(decimalToHexadecimal(0)).toBe('0')
+  })
+
+  test("decimalToHexadecimal(10) returns 'A'", () => {
+    expect(decimalToHexadecimal(10)).toBe('A')
+  })
+
+  test("decimalToHexadecimal(15) returns 'F'", () => {
+    expect(decimalToHexadecimal(15)).toBe('F')
+  })
+
+  test("decimalToHexadecimal(16) returns '10'", () => {
+    expect(decimalToHexadecimal(16)).toBe('10')
+  })
+
+  test("decimalToHexadecimal(255) returns 'FF'", () => {
+    expect(decimalToHexadecimal(255)).toBe('FF')
+  })
+
+  test("decimalToHexadecimal(256) returns '100'", () => {
+    expect(decimalToHexadecimal(256)).toBe('100')
+  })
+
+  test("decimalToHexadecimal(4096) returns '1000'", () => {
+    expect(decimalToHexadecimal(4096)).toBe('1000')
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => decimalToHexadecimal(-1)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => decimalToHexadecimal(1.5)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => decimalToHexadecimal('FF')).toThrow(TypeError)
+  })
+})