Refactor: es2016nify (#6)

* Use Default Parametor

* let to const

* Use Rest Parametor

* Use Destructuring assignment

* Use arrow function

lib/i18n.js

@@ -1,10 +1,8 @@
 'use strict';
 
-const vsprintf = require('sprintf-js').vsprintf;
-
-function i18n(options) {
-  options = options || {};
+const { vsprintf } = require('sprintf-js');
 
+function i18n(options = {}) {
   this.data = {};
   this.languages = options.languages || ['default'];
 
@@ -14,9 +12,8 @@ function i18n(options) {
 }
 
 i18n.prototype.get = function(languages) {
-  const data = this.data;
+  const { data } = this;
   const result = {};
-  let lang, langData, keys, key, i, leni, j, lenj;
 
   if (languages) {
     if (!Array.isArray(languages)) {
@@ -26,15 +23,15 @@ i18n.prototype.get = function(languages) {
     languages = this.languages;
   }
 
-  for (i = 0, leni = languages.length; i < leni; i++) {
-    lang = languages[i];
-    langData = data[lang];
+  for (let i = 0, leni = languages.length; i < leni; i++) {
+    const lang = languages[i];
+    const langData = data[lang];
     if (!langData) continue;
 
-    keys = Object.keys(langData);
+    const keys = Object.keys(langData);
 
-    for (j = 0, lenj = keys.length; j < lenj; j++) {
-      key = keys[j];
+    for (let j = 0, lenj = keys.length; j < lenj; j++) {
+      const key = keys[j];
       if (!result.hasOwnProperty(key)) result[key] = langData[key];
     }
   }
@@ -63,17 +60,12 @@ i18n.prototype.list = function() {
   return Object.keys(this.data);
 };
 
-function flattenObject(data, obj, parent) {
-  obj = obj || {};
-  parent = parent || '';
-
+function flattenObject(data, obj = {}, parent = '') {
   const keys = Object.keys(data);
-  let key = '';
-  let item;
 
   for (let i = 0, len = keys.length; i < len; i++) {
-    key = keys[i];
-    item = data[key];
+    const key = keys[i];
+    const item = data[key];
 
     if (typeof item === 'object') {
       flattenObject(item, obj, parent + key + '.');
@@ -88,17 +80,9 @@ function flattenObject(data, obj, parent) {
 i18n.prototype.__ = function(lang) {
   const data = this.get(lang);
 
-  return function() {
-    const len = arguments.length;
-    if (!len) return '';
-
-    const args = new Array(len);
-
-    for (let i = 0; i < len; i++) {
-      args[i] = arguments[i];
-    }
+  return (key, ...args) => {
+    if (!key) return '';
 
-    const key = args.shift();
     const str = data[key] || key;
 
     return vsprintf(str, args);
@@ -108,17 +92,9 @@ i18n.prototype.__ = function(lang) {
 i18n.prototype._p = function(lang) {
   const data = this.get(lang);
 
-  return function() {
-    const len = arguments.length;
-    if (!len) return '';
-
-    const args = new Array(len);
-
-    for (let i = 0; i < len; i++) {
-      args[i] = arguments[i];
-    }
+  return (key, ...args) => {
+    if (!key) return '';
 
-    const key = args.shift();
     const number = args.length ? +args[0] : 0;
     let str = key;