feat: support custom renderers

mod.ts

@@ -12,7 +12,7 @@ export { CSS, KATEX_CSS, Marked };
 
 Marked.marked.use(gfmHeadingId());
 
-class Renderer extends Marked.Renderer {
+export class Renderer extends Marked.Renderer {
   allowMath: boolean;
 
   constructor(options: Marked.marked.MarkedOptions & RenderOptions = {}) {
@@ -104,6 +104,7 @@ export interface RenderOptions {
   allowIframes?: boolean;
   allowMath?: boolean;
   disableHtmlSanitization?: boolean;
+  renderer?: Renderer;
 }
 
 export function render(markdown: string, opts: RenderOptions = {}): string {
@@ -117,7 +118,7 @@ export function render(markdown: string, opts: RenderOptions = {}): string {
     baseUrl: opts.baseUrl,
     gfm: true,
     mangle: false,
-    renderer: new Renderer(opts),
+    renderer: opts.renderer ? opts.renderer : new Renderer(opts),
   };
 
   const html = opts.inline

test/test.ts

@@ -1,6 +1,6 @@
 import { assertEquals } from "https://deno.land/std@0.178.0/testing/asserts.ts";
 import { DOMParser } from "https://deno.land/x/deno_dom@v0.1.35-alpha/deno-dom-wasm.ts";
-import { render } from "../mod.ts";
+import { render, Renderer } from "../mod.ts";
 
 Deno.test("Basic markdown", async () => {
   const markdown = await Deno.readTextFile("./test/fixtures/basic.md");
@@ -79,3 +79,20 @@ Deno.test(
     assertEquals(html, expected);
   },
 );
+
+Deno.test(
+  "custom renderer",
+  () => {
+    const markdown = `# hello world`;
+    const expected = `<h1 id="custom-renderer">hello world</h1>`;
+
+    class CustomRenderer extends Renderer {
+      heading(text: string, level: 1 | 2 | 3 | 4 | 5 | 6): string {
+        return `<h${level} id="custom-renderer">${text}</h${level}>`;
+      }
+    }
+
+    const html = render(markdown, { renderer: new CustomRenderer({}) });
+    assertEquals(html, expected);
+  },
+);