Implicitly set precision through smallest set unit

Author: ad-si

source/index.js

@@ -37,7 +37,6 @@ export default class Duration {
 			let value = Number(durationArray[index + 1])
 
 			if (typeof value === 'number' && !Number.isNaN(value)) {
-				this._precision = fragment.replace(/s$/, '')
 				this[fragment] = value
 			}
 		})
@@ -79,7 +78,23 @@ export default class Duration {
 	}
 
 
-	get precision () { return this._precision }
+	get precision () {
+		let precision
+
+		// Clone array as .reverse() is in place
+		Array.from(durationFragments)
+			.reverse()
+			.some(fragment => {
+				const value = this[fragment]
+
+				if (typeof value === 'number' && !Number.isNaN(value)) {
+					precision = fragment.replace(/s$/, '')
+					return true
+				}
+			})
+
+		return precision
+	}
 	set precision (precision) {
 		this._precision = precision
 		return this

test/precision.js

@@ -1,12 +1,17 @@
 import runTest from 'ava'
 import expect from 'unexpected'
-import Duration from '../source/index.js'
+import Duration from '../source/index'
 
 runTest('precision of P7D is day', test => {
 	const duration = new Duration('P7D')
 	expect(duration.precision, 'to equal', 'day')
 })
 
+runTest('precision of P5Y is year', test => {
+	const duration = new Duration('P5Y')
+	expect(duration.precision, 'to equal', 'year')
+})
+
 runTest('precision of P7D0H is hour', test => {
 	const duration = new Duration('P7D0H')
 	expect(duration.precision, 'to equal', 'hour')