[feat]: add marked extensions support (#227)

* feat: add marked:extensions support

* test: fix typo

* test(extensions): add marked:extensions test

* docs(extensions): add extensions example

Author: Eumeryx

README.md

@@ -233,6 +233,39 @@ hexo.extend.filter.register('marked:tokenizer', function(tokenizer) {
 });
 ```
 
+#### Extensions
+
+It is also possible to customize the [extensions](https://marked.js.org/using_pro#extensions).
+For example, use [KaTeX](https://katex.org/) to render block-level math:
+
+```js
+const katex = require('katex');
+
+hexo.extend.filter.register('marked:extensions', function(extensions) {
+  // Info: `extensions` is an array.
+  extensions.push({
+    name: 'blockMath',
+    level: 'block',
+    tokenizer(src) {
+      const cap = /^\s{0,3}\$\$((?:[^\n]|\n[^\n])+?)\n{0,1}\$\$/.exec(src);
+
+      if (cap !== null) {
+        return {
+          type: 'blockMath',
+          raw: cap[0],
+          math: cap[1]
+        };
+      }
+
+      return undefined;
+    },
+    renderer(token) {
+      return `<p>${katex.renderToString(token.math, {displayMode: true})}</p>\n`;
+    }
+  });
+});
+```
+
 [Markdown]: https://daringfireball.net/projects/markdown/
 [marked]: https://github.com/chjj/marked
 [PHP Markdown Extra]: https://michelf.ca/projects/php-markdown/extra/#def-list

lib/renderer.js

@@ -213,6 +213,10 @@ module.exports = function(data, options) {
   const tokenizer = new Tokenizer();
   this.execFilterSync('marked:tokenizer', tokenizer, {context: this});
 
+  const extensions = [];
+  this.execFilterSync('marked:extensions', extensions, {context: this});
+  marked.use({extensions});
+
   let postPath = '';
   if (path && post_asset_folder && prependRoot && postAsset) {
     const Post = this.model('Post');

test/index.js

@@ -899,7 +899,7 @@ describe('Marked renderer', () => {
       ].join('\n'));
     });
 
-    it('should execute filter registered to marked:renderer', () => {
+    it('should execute filter registered to marked:tokenizer', () => {
       const smartypants = str => {
         return str.replace(/---/g, '\u2014');
       };
@@ -921,6 +921,38 @@ describe('Marked renderer', () => {
       const result = r({text: body});
       result.should.eql(`<p>${smartypants(body)}</p>\n`);
     });
+
+    it('should execute filter registered to marked:extensions', () => {
+      hexo.extend.filter.register('marked:extensions', extensions => {
+        extensions.push({
+          name: 'blockMath',
+          level: 'block',
+          tokenizer(src) {
+            const cap = /^\s{0,3}\$\$((?:[^\n]|\n[^\n])+?)\n{0,1}\$\$/.exec(src);
+
+            if (cap !== null) {
+              return {
+                type: 'blockMath',
+                raw: cap[0],
+                math: cap[1]
+              };
+            }
+
+            return undefined;
+          },
+          renderer(token) {
+            return `<p class="math block">${escapeHTML(token.math)}</p>\n`;
+          }
+        });
+      });
+
+      const body = '$$E=mc^2$$';
+
+      const r = require('../lib/renderer').bind(hexo);
+
+      const result = r({text: body});
+      result.should.eql(`<p class="math block">${escapeHTML('E=mc^2')}</p>\n`);
+    });
   });
 
   describe('nunjucks', () => {