postprocess revealjs slides so that anchor clicks resolve correctly (#4623)

* postprocess revealjs slides so that anchor clicks resolve correctly. Closes #3533
* be more defensive in case slides have no id

Author: cscheid

news/changelog-1.3.md

@@ -54,6 +54,7 @@
 - Authors on the title slides now correctly object customization of the `$presentation-title-slide-text-align` scss variable ([#3843](https://github.com/quarto-dev/quarto-cli/issues/3843))
 - Properly support `show-notes: separate-page` [#3996](https://github.com/quarto-dev/quarto-cli/issues/3996)
 - Improve footnote / aside layout for centered slides. [#4297](https://github.com/quarto-dev/quarto-cli/issues/4297)
+- Ensure anchors refer to the containing slide in case of crossrefs ([#3533](https://github.com/quarto-dev/quarto-cli/issues/4297)).
 
 ## EPUB Format
 

src/format/reveal/format-reveal.ts

@@ -682,6 +682,23 @@ function revealHtmlPostprocessor(
       }
     }
 
+    // https://github.com/quarto-dev/quarto-cli/issues/3533
+    // redirect anchors to the slide they refer to
+    const anchors = doc.querySelectorAll("a[href^='#/']");
+    for (const anchor of anchors) {
+      const anchorEl = anchor as Element;
+      const href = anchorEl.getAttribute("href");
+      if (href) {
+        const target = doc.getElementById(href.replace(/^#\//, ""));
+        if (target) {
+          const slide = findParentSlide(target);
+          if (slide && slide.getAttribute("id")) {
+            anchorEl.setAttribute("href", `#/${slide.getAttribute("id")}`);
+          }
+        }
+      }
+    }
+
     // return result
     return Promise.resolve(result);
   };