Add precision property, handle invalid duration strings

Author: ad-si

.babelrc

@@ -0,0 +1,8 @@
+{
+	"presets" : [
+		"babel-preset-es2015"
+	],
+	"plugins": [
+		"syntax-trailing-function-commas"
+	]
+}

package.json

@@ -7,9 +7,9 @@
     "test": "test"
   },
   "scripts": {
-    "build": "babel --quiet --presets es2015 source --out-dir build",
-    "test": "npm run build && ava --fail-fast",
-    "prepublish": "npm test"
+    "build": "babel --quiet source --out-dir build",
+    "test": "ava --require babel-register --fail-fast",
+    "prepublish": "npm test && npm run build"
   },
   "keywords": [
     "duration",
@@ -21,6 +21,7 @@
     "ava": "^0.12.0",
     "babel-cli": "^6.6.5",
     "babel-preset-es2015": "^6.6.0",
+    "babel-register": "^6.6.5",
     "unexpected": "^10.4.0"
   },
   "repository": {

source/index.js

@@ -3,7 +3,7 @@ import durationFragments from './fragments'
 export default class Duration {
 	constructor (durationString) {
 		let durationPattern =
-			'P' +
+			'^P' +
 			'(?:(\\d+)Y)?' + // Years
 			'(?:(\\d+)M)?' + // Months
 			'(?:(\\d+)W)?' + // Weeks
@@ -12,18 +12,32 @@ export default class Duration {
 			'(?:(\\d+)H)?' + // Hours
 			'(?:(\\d+)M)?' + // Minutes
 			'(?:(\\d+)?' +   // Seconds
-			'\\.?(\\d+)?S)?' // Milliseconds
+			'\\.?(\\d+)?S)?' + // Milliseconds
+			'$'
 
 		let regex = new RegExp(durationPattern, 'i')
 		let durationArray = durationString.match(regex)
 
+		if (!durationArray) {
+			throw new Error(`"${durationString}" is an invalid duration string`)
+		}
+
 		durationFragments.forEach((fragment, index) => {
 			let value = Number(durationArray[index + 1])
-			if (value)
+
+			if (typeof value === 'number' && !Number.isNaN(value)) {
+				this._precision = fragment.replace('s', '')
 				this[fragment] = value
+			}
 		})
 	}
 
+	get precision () { return this._precision }
+	set precision (precision) {
+		this._precision = precision
+		return this
+	}
+
 	get string () {
 		return durationFragments
 			.reduce(

test/precision.js

@@ -0,0 +1,13 @@
+import runTest from 'ava'
+import expect from 'unexpected'
+import Duration from '../source/index.js'
+
+runTest('precision of P7D is day', test => {
+	const duration = new Duration('P7D')
+	expect(duration.precision, 'to equal', 'day')
+})
+
+runTest('precision of P7D0H is hour', test => {
+	const duration = new Duration('P7D0H')
+	expect(duration.precision, 'to equal', 'hour')
+})