feat: add speed conversion kmph to mph and mph to kmph

Conversions/SpeedConversion.js

@@ -0,0 +1,33 @@
+/**
+ * @function kmphToMph
+ * @description Converts speed from kilometers per hour to miles per hour.
+ * @param {number} kmph - Speed in kilometers per hour
+ * @returns {number} - Speed in miles per hour
+ * @see https://en.wikipedia.org/wiki/Miles_per_hour
+ * @example kmphToMph(1) => 0.621371
+ * @example kmphToMph(100) => 62.1371
+ */
+const kmphToMph = (kmph) => {
+  if (typeof kmph !== 'number' || isNaN(kmph)) {
+    throw new TypeError('Input must be a number')
+  }
+  return kmph * 0.621371
+}
+
+/**
+ * @function mphToKmph
+ * @description Converts speed from miles per hour to kilometers per hour.
+ * @param {number} mph - Speed in miles per hour
+ * @returns {number} - Speed in kilometers per hour
+ * @see https://en.wikipedia.org/wiki/Kilometres_per_hour
+ * @example mphToKmph(1) => 1.60934
+ * @example mphToKmph(60) => 96.5604
+ */
+const mphToKmph = (mph) => {
+  if (typeof mph !== 'number' || isNaN(mph)) {
+    throw new TypeError('Input must be a number')
+  }
+  return mph * 1.60934
+}
+
+export { kmphToMph, mphToKmph }

Conversions/test/SpeedConversion.test.js

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+import { kmphToMph, mphToKmph } from '../SpeedConversion.js'
+
+describe('kmphToMph', () => {
+  test('kmphToMph(0) returns 0', () => {
+    expect(kmphToMph(0)).toBe(0)
+  })
+
+  test('kmphToMph(1) returns 0.621371', () => {
+    expect(kmphToMph(1)).toBeCloseTo(0.621371)
+  })
+
+  test('kmphToMph(100) returns 62.1371', () => {
+    expect(kmphToMph(100)).toBeCloseTo(62.1371)
+  })
+
+  test('kmphToMph(-60) works for negative values', () => {
+    expect(kmphToMph(-60)).toBeCloseTo(-37.28226)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => kmphToMph('100')).toThrow(TypeError)
+  })
+
+  test('throws TypeError for NaN', () => {
+    expect(() => kmphToMph(NaN)).toThrow(TypeError)
+  })
+})
+
+describe('mphToKmph', () => {
+  test('mphToKmph(0) returns 0', () => {
+    expect(mphToKmph(0)).toBe(0)
+  })
+
+  test('mphToKmph(1) returns 1.60934', () => {
+    expect(mphToKmph(1)).toBeCloseTo(1.60934)
+  })
+
+  test('mphToKmph(60) returns 96.5604', () => {
+    expect(mphToKmph(60)).toBeCloseTo(96.5604)
+  })
+
+  test('mphToKmph(-30) works for negative values', () => {
+    expect(mphToKmph(-30)).toBeCloseTo(-48.2802)
+  })
+
+  test('throws TypeError for non-number input', () => {
+    expect(() => mphToKmph('60')).toThrow(TypeError)
+  })
+
+  test('throws TypeError for NaN', () => {
+    expect(() => mphToKmph(NaN)).toThrow(TypeError)
+  })
+})