feat: add inches to metric conversion (#226)

Closes #225

src/inches-to-metric.js

@@ -0,0 +1,25 @@
+export default inchesToMetric
+
+const cmConversion = 2.54
+
+const mapper = {
+  cm: cmConversion,
+  m: cmConversion / 100,
+  mm: cmConversion * 10,
+}
+
+function inchesToMetric(value, unit = 'cm') {
+  if (isNaN(value)) {
+    throw new TypeError('First argument must be of type "number"')
+  }
+
+  if (value > 12 || value < 0) {
+    throw new RangeError('Inches have to be between 0 and 12')
+  }
+
+  if (!mapper[unit]) {
+    throw new Error('Can only convert inches to meters ("m"), centimeters ("cm"), or milimeters ("mm").')
+  }
+
+  return value * mapper[unit]
+}

src/index.js

@@ -84,6 +84,7 @@ import timeSince from './timeSince'
 import first from './first'
 import mode from './mode-array'
 import rollDice from './rollDice'
+import inchesToMetric from './inches-to-metric'
 
 export {
   reverseArrayInPlace,
@@ -172,4 +173,5 @@ export {
   first,
   mode,
   rollDice,
+  inchesToMetric,
 }

test/inches-to-metric.js

@@ -0,0 +1,30 @@
+import test from 'ava'
+import {inchesToMetric} from './../src'
+
+test('should throw error if a number is not passed', t => {
+  t.throws(() => inchesToMetric('foo'))
+})
+
+test('should throw error if inches is out of range value', t => {
+  t.throws(() => inchesToMetric(22))
+  t.throws(() => inchesToMetric(-1))
+})
+
+test('should throw error if wrong metric value is passed', t => {
+  t.throws(() => inchesToMetric(12, 'km'))
+})
+
+test('should convert inches to centimeters', t => {
+  t.deepEqual(inchesToMetric(1), 2.54)
+  t.deepEqual(inchesToMetric(10), 25.4)
+})
+
+test('should convert inches to meters', t => {
+  t.deepEqual(inchesToMetric(1, 'm'), 0.0254)
+  t.deepEqual(inchesToMetric(10, 'm'), 0.254)
+})
+
+test('should convert inches to milimeters', t => {
+  t.deepEqual(inchesToMetric(1, 'mm'), 25.4)
+  t.deepEqual(inchesToMetric(10, 'mm'), 254)
+})