refactor(open_graph): drop cheerio and use regex (hexojs#3680)

* refactor(open_graph): drop cheerio and use regex

* feat(open_graph): faster regex pattern for img tag

* refactor(open_graph): eliminate unnecessary checks

* feat(open_graph): a new regex which use less steps

* test(open_graph): add img with empty src attribute

lib/plugins/helper/open_graph.js

@@ -3,7 +3,6 @@
 const urlFn = require('url');
 const moment = require('moment');
 const { escapeHTML, htmlTag, stripHTML } = require('hexo-util');
-let cheerio;
 
 function meta(name, content, escape) {
   if (escape !== false && typeof content === 'string') {
@@ -28,7 +27,6 @@ function og(name, content, escape) {
 }
 
 function openGraphHelper(options = {}) {
-  if (!cheerio) cheerio = require('cheerio');
 
   const { config, page } = this;
   const { content } = page;
@@ -59,12 +57,14 @@ function openGraphHelper(options = {}) {
   if (!images.length && content) {
     images = images.slice();
 
-    const $ = cheerio.load(content);
+    if (content.includes('<img')) {
+      let img;
+      const imgPattern = /<img [^>]*src=['"]([^'"]+)([^>]*>)/gi;
+      while ((img = imgPattern.exec(content)) !== null) {
+        images.push(img[1]);
+      }
+    }
 
-    $('img').each(function() {
-      const src = $(this).attr('src');
-      if (src) images.push(src);
-    });
   }
 
   let result = '';

test/scripts/helpers/open_graph.js

@@ -118,7 +118,9 @@ describe('open_graph', () => {
       page: {
         content: [
           '<p>123456789</p>',
-          '<img src="https://hexo.io/test.jpg">'
+          '<img src="https://hexo.io/test.jpg">',
+          '<img src="">',
+          '<img class="img">'
         ].join('')
       },
       config: hexo.config,
@@ -163,7 +165,9 @@ describe('open_graph', () => {
       page: {
         content: [
           '<p>123456789</p>',
-          '<img src="https://hexo.io/test.jpg">'
+          '<img src="https://hexo.io/test.jpg">',
+          '<img src="">',
+          '<img class="img">'
         ].join(''),
         photos: []
       },