refactor: drop lodash & es6 syntax for lib/theme

lib/theme/index.js

@@ -1,11 +1,10 @@
 'use strict';
 
 const { extname } = require('path');
-const util = require('util');
+const { inherits } = require('util');
 const Box = require('../box');
 const View = require('./view');
 const I18n = require('hexo-i18n');
-const _ = require('lodash');
 
 function Theme(ctx) {
   Reflect.apply(Box, this, [ctx, ctx.theme_dir]);
@@ -28,7 +27,7 @@ function Theme(ctx) {
   languages.push('default');
 
   this.i18n = new I18n({
-    languages: _(languages).compact().uniq().value()
+    languages: [...new Set(languages.filter(Boolean))]
   });
 
   const viewFn = function(path, data) {
@@ -38,14 +37,14 @@ function Theme(ctx) {
   const _View = viewFn;
   this.View = viewFn;
 
-  util.inherits(_View, View);
+  inherits(_View, View);
 
   _View.prototype._theme = this;
   _View.prototype._render = ctx.render;
   _View.prototype._helper = ctx.extend.helper;
 }
 
-util.inherits(Theme, Box);
+inherits(Theme, Box);
 
 Theme.prototype.getView = function(path) {
   // Replace backslashes on Windows

lib/theme/view.js

@@ -2,7 +2,6 @@
 
 const { dirname, extname, join } = require('path');
 const assignIn = require('lodash/assignIn');
-const omit = require('lodash/omit');
 const yfm = require('hexo-front-matter');
 const Promise = require('bluebird');
 
@@ -61,7 +60,9 @@ View.prototype.renderSync = function(options = {}) {
 };
 
 View.prototype._buildLocals = function(locals) {
-  return assignIn({}, locals, omit(this.data, ['layout', '_content']), {
+  // eslint-disable-next-line no-unused-vars
+  const { layout, _content, ...data } = this.data;
+  return assignIn({}, locals, data, {
     filename: this.source
   });
 };
@@ -70,8 +71,7 @@ View.prototype._bindHelpers = function(locals) {
   const helpers = this._helper.list();
   const keys = Object.keys(helpers);
 
-  for (let i = 0, len = keys.length; i < len; i++) {
-    const key = keys[i];
+  for (const key of keys) {
     locals[key] = helpers[key].bind(locals);
   }