feat: adds yaml frontmatter support

package.json

@@ -47,5 +47,8 @@
     "typedoc": "^0.23.9",
     "typescript": "^4.7.4",
     "uglify-js": "^3.16.3"
+  },
+  "dependencies": {
+    "yaml": "^2.4.5"
   }
 }

src/defaults.ts

@@ -5,6 +5,7 @@ import { codeblockRenderer } from './renderers/codeblock';
 import { dlRenderer } from './renderers/dl';
 import { emojiRenderer } from './renderers/emoji';
 import { footnoteRenderer } from './renderers/footnote';
+import { frontmatter, frontmatterRenderer } from './renderers/frontmatter';
 import { h1Renderer } from './renderers/h1';
 import { h2Renderer } from './renderers/h2';
 import { h3Renderer } from './renderers/h3';
@@ -18,7 +19,6 @@ import { italicRenderer } from './renderers/italic';
 import { linkRenderer } from './renderers/link';
 import { olRenderer } from './renderers/ol';
 import { pRenderer } from './renderers/p';
-import { strikethroughRenderer } from './renderers/strikethrough';
 import {
   bigintRenderer,
   booleanRenderer,
@@ -28,6 +28,7 @@ import {
   stringRenderer,
   undefinedRenderer,
 } from './renderers/primitives';
+import { strikethroughRenderer } from './renderers/strikethrough';
 import { subRenderer } from './renderers/sub';
 import { supRenderer } from './renderers/sup';
 import { tableRenderer } from './renderers/table';
@@ -79,6 +80,7 @@ export function getRenderers(customRenderers: Renderers = {}): Renderers {
     tasks: tasksRenderer,
     text: textRenderer,
     ul: ulRenderer,
+    frontmatter: frontmatterRenderer,
     ...customRenderers,
   };
 }

src/renderers/frontmatter.test.ts

@@ -0,0 +1,32 @@
+import { tsMarkdown } from '../rendering';
+import { FrontmatterEntry, frontmatter } from './frontmatter';
+
+describe('given a frontmatter entry', () => {
+  describe('with an object value', () => {
+    const entry: FrontmatterEntry = {
+      frontmatter: {
+        date: '1970-01-01',
+      },
+    };
+
+    test('renders a frontmatter header with the specified object as content', () => {
+      expect(tsMarkdown([entry])).toBe(
+        `---\n${Object.keys(entry.frontmatter)[0]}: ${
+          Object.values(entry.frontmatter)[0]
+        }\n---`
+      );
+    });
+  });
+
+  describe('using a helper with an object value', () => {
+    const entry = frontmatter({ date: '1970-01-01' });
+
+    test('renders a frontmatter header with the specified object as content', () => {
+      expect(tsMarkdown([entry])).toBe(
+        `---\n${Object.keys(entry.frontmatter)[0]}: ${
+          Object.values(entry.frontmatter)[0]
+        }\n---`
+      );
+    });
+  });
+});

src/renderers/frontmatter.ts

@@ -0,0 +1,40 @@
+import { stringify } from 'yaml';
+import { getMarkdownString } from '../rendering';
+import { MarkdownRenderer, RenderOptions } from '../rendering.types';
+import { MarkdownEntry } from '../shared.types';
+
+/**
+ * Markdown entry for generating frontmatter elements
+ */
+export interface FrontmatterEntry extends MarkdownEntry {
+  frontmatter: Object;
+}
+
+/**
+ * Renderer for frontmatter entries
+ *
+ * @param entry the frontmatter object entry
+ * @param options
+ * @returns
+ */
+export const frontmatterRenderer: MarkdownRenderer = (
+  entry: FrontmatterEntry
+) => {
+  if ('frontmatter' in entry) {
+    const frontmatterText = stringify(entry.frontmatter);
+    return {
+      markdown: `---\n${frontmatterText}---`,
+      blockLevel: true,
+    };
+  }
+
+  throw new Error('Entry is not a frontmatter object. Unable to render');
+};
+
+export function frontmatter(
+  content: FrontmatterEntry['frontmatter']
+): FrontmatterEntry {
+  return {
+    frontmatter: content,
+  };
+}