feat: support frontmatter preprocess

src/head.ts

@@ -0,0 +1,33 @@
+import { ResolvedOptions } from './types'
+
+export function preprocessHead(frontmatter: any, options: ResolvedOptions) {
+  if (!options.headEnabled)
+    return frontmatter
+
+  const head = options.headField ? frontmatter.head || {} : frontmatter
+
+  const meta = head.meta = head.meta || []
+
+  if (head.title) {
+    if (!meta.find((i: any) => i.property === 'og:title'))
+      meta.push({ property: 'og:title', content: head.title })
+  }
+
+  if (head.description) {
+    if (!meta.find((i: any) => i.property === 'og:description'))
+      meta.push({ property: 'og:description', content: head.description })
+
+    if (!meta.find((i: any) => i.name === 'description'))
+      meta.push({ name: 'description', content: head.description })
+  }
+
+  if (head.image) {
+    if (!meta.find((i: any) => i.property === 'og:image'))
+      meta.push({ property: 'og:image', content: head.image })
+
+    if (!meta.find((i: any) => i.property === 'twitter:card'))
+      meta.push({ name: 'twitter:card', content: 'summary_large_image' })
+  }
+
+  return frontmatter
+}

src/markdown.ts

@@ -32,12 +32,14 @@ export function createMarkdown(options: ResolvedOptions) {
   options.markdownItSetup(markdown)
 
   return (id: string, raw: string) => {
-    const { wrapperClasses, wrapperComponent, transforms, headEnabled, headField } = options
+    const { wrapperClasses, wrapperComponent, transforms, headEnabled, headField, frontmatterPreprocess } = options
 
     if (transforms.before)
       raw = transforms.before(raw, id)
 
-    const { content: md, data: frontmatter } = matter(raw)
+    const { content: md, data } = matter(raw)
+    const frontmatter = frontmatterPreprocess(data, options)
+
     let html = markdown.render(md, {})
 
     if (wrapperClasses)

src/options.ts

@@ -1,3 +1,4 @@
+import { preprocessHead } from './head'
 import { Options, ResolvedOptions } from './types'
 import { toArray } from './utils'
 
@@ -11,6 +12,7 @@ export function resolveOptions(userOptions: Options): ResolvedOptions {
     wrapperClasses: 'markdown-body',
     wrapperComponent: null,
     transforms: {},
+    frontmatterPreprocess: preprocessHead,
   }, userOptions) as ResolvedOptions
 
   options.wrapperClasses = toArray(options.wrapperClasses).filter(i => i).join(' ')

src/types.ts

@@ -1,3 +1,4 @@
+/* eslint-disable no-use-before-define */
 import type MarkdownIt from 'markdown-it'
 
 export interface Options {
@@ -15,6 +16,12 @@ export interface Options {
    * @default ''
    */
   headField?: string
+
+  /**
+   * Custom function to process the frontmatter
+   */
+  frontmatterPreprocess?: (frontmatter: any, options: ResolvedOptions) => any
+
   /**
    * Options passed to Markdown It
    */