feat: support async transformers (#60)

Author: kermanx

src/core/markdown.ts

@@ -107,7 +107,7 @@ export function createMarkdown(options: ResolvedOptions) {
     } = options
 
     raw = raw.trimStart()
-    raw = transforms.before?.(raw, id) ?? raw
+    raw = await transforms.before?.(raw, id) ?? raw
 
     const env: MarkdownEnv = { id }
     let html = await markdown.renderAsync(raw, env)
@@ -138,7 +138,7 @@ export function createMarkdown(options: ResolvedOptions) {
       html = `<${wrapperComponentName} ${attrs}>${html}</${wrapperComponentName}>`
     }
 
-    html = transforms.after?.(html, id) ?? html
+    html = await transforms.after?.(html, id) ?? html
 
     if (options.escapeCodeTagInterpolation) {
       // escape curly brackets interpolation in <code>, #14
@@ -194,7 +194,7 @@ export function createMarkdown(options: ResolvedOptions) {
         scriptLines.push('useHead(head)')
       }
 
-      scriptLines.push(...transforms.extraScripts?.(frontmatter, id) || [])
+      scriptLines.push(...await transforms.extraScripts?.(frontmatter, id) || [])
     }
 
     if (options.excerpt) {

src/types.ts

@@ -187,12 +187,12 @@ export interface Options {
    * Custom tranformations apply before and after the markdown transformation
    */
   transforms?: {
-    before?: (code: string, id: string) => string
-    after?: (code: string, id: string) => string
+    before?: (code: string, id: string) => string | Promise<string>
+    after?: (code: string, id: string) => string | Promise<string>
     /**
      * Return extra code to be injected into the `<script>` tag
      */
-    extraScripts?: (frontmatter: Record<string, any>, id: string) => string[]
+    extraScripts?: (frontmatter: Record<string, any>, id: string) => string[] | Promise<string[]>
   }
 
   include?: FilterPattern