feat: add Fahrenheit to Celsius conversion

Conversions/FahrenheitToCelsius.js

@@ -0,0 +1,19 @@
+/**
+ * @function fahrenheitToCelsius
+ * @description Converts a temperature from Fahrenheit to Celsius.
+ *   The formula is: C = (F - 32) × 5/9
+ * @param {number} fahrenheit - Temperature in Fahrenheit
+ * @returns {number} - Temperature in Celsius
+ * @see https://en.wikipedia.org/wiki/Celsius
+ * @example fahrenheitToCelsius(32) => 0
+ * @example fahrenheitToCelsius(212) => 100
+ * @example fahrenheitToCelsius(-40) => -40
+ */
+const fahrenheitToCelsius = (fahrenheit) => {
+  if (typeof fahrenheit !== 'number' || isNaN(fahrenheit)) {
+    throw new TypeError('Input must be a number')
+  }
+  return ((fahrenheit - 32) * 5) / 9
+}
+
+export { fahrenheitToCelsius }

Conversions/test/FahrenheitToCelsius.test.js

@@ -0,0 +1,35 @@
+import { fahrenheitToCelsius } from '../FahrenheitToCelsius.js'
+
+describe('fahrenheitToCelsius', () => {
+  test('fahrenheitToCelsius(32) returns 0', () => {
+    expect(fahrenheitToCelsius(32)).toBe(0)
+  })
+
+  test('fahrenheitToCelsius(212) returns 100', () => {
+    expect(fahrenheitToCelsius(212)).toBe(100)
+  })
+
+  test('fahrenheitToCelsius(-40) returns -40', () => {
+    expect(fahrenheitToCelsius(-40)).toBe(-40)
+  })
+
+  test('fahrenheitToCelsius(98.6) returns 37', () => {
+    expect(fahrenheitToCelsius(98.6)).toBeCloseTo(37)
+  })
+
+  test('fahrenheitToCelsius(68) returns 20', () => {
+    expect(fahrenheitToCelsius(68)).toBeCloseTo(20)
+  })
+
+  test('fahrenheitToCelsius(-459.67) returns -273.15', () => {
+    expect(fahrenheitToCelsius(-459.67)).toBeCloseTo(-273.15)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => fahrenheitToCelsius('32')).toThrow(TypeError)
+  })
+
+  test('throws TypeError for NaN', () => {
+    expect(() => fahrenheitToCelsius(NaN)).toThrow(TypeError)
+  })
+})