feat(export/markdown): export in-line math properly

src/services/export/markdown.spec.ts

@@ -279,4 +279,10 @@ describe("Markdown export", () => {
         expect(markdownExportService.toMarkdown(html)).toBe(expected);
     });
 
+    it("converts inline math expressions to proper Markdown syntax", () => {
+        const html = /*html*/`<p>The equation is&nbsp;<span class="math-tex">\(e=mc^{2}\)</span>.</p>`;
+        const expected = `The equation is\u00a0$e=mc^{2}$.`;
+        expect(markdownExportService.toMarkdown(html)).toBe(expected);
+    });
+
 });

src/services/export/markdown.ts

@@ -46,6 +46,7 @@ function toMarkdown(content: string) {
         instance.addRule("admonition", buildAdmonitionFilter());
         instance.addRule("inlineLink", buildInlineLinkFilter());
         instance.addRule("figure", buildFigureFilter());
+        instance.addRule("math", buildMathFilter());
         instance.use(gfm);
         instance.keep([ "kbd" ]);
     }
@@ -207,6 +208,23 @@ function buildFigureFilter(): Rule {
     }
 }
 
+function buildMathFilter(): Rule {
+    return {
+        filter(node) {
+            return node.nodeName === "SPAN" && node.classList.contains("math-tex");
+        },
+        replacement(content) {
+            // Inline math
+            if (content.startsWith("(") && content.endsWith(")")) {
+                return `$${content.substring(1, content.length - 1)}$`;
+            }
+
+            // Unknown.
+            return content;
+        }
+    }
+}
+
 // Taken from upstream since it's not exposed.
 // https://github.com/mixmark-io/turndown/blob/master/src/commonmark-rules.js
 function cleanAttribute(attribute: string | null | undefined) {