Add local JavaScript fix for collapse scroll positioning issue

Co-authored-by: mmcky <8263752+mmcky@users.noreply.github.com>

Author: Copilot

lectures/_config.yml

@@ -75,6 +75,7 @@ sphinx:
     html_favicon: _static/lectures-favicon.ico
     html_theme: quantecon_book_theme
     html_static_path: ['_static']
+    html_js_files: ['collapse-fix.js']
     html_theme_options:
       authors:
         - name: Thomas J. Sargent

lectures/_static/collapse-fix.js

@@ -0,0 +1,98 @@
+/* 
+ * Fix for collapse scroll positioning issue
+ * This script improves the scroll behavior when collapsing code blocks
+ * for better reading continuity.
+ * 
+ * The issue: when clicking collapse, the code block gets positioned too high
+ * in the viewport, interrupting the reading flow.
+ * 
+ * The solution: position the collapsed code block so its bottom is roughly
+ * 1/3 from the top of the viewport, leaving visible content below for
+ * continuous reading.
+ */
+
+document.addEventListener("DOMContentLoaded", function () {
+  // Wait for the theme's JavaScript to load and set up collapse functionality
+  setTimeout(() => {
+    console.log('Applying collapse scroll behavior fix...');
+    
+    const collapsableCodeToggles = document.querySelectorAll(
+      "div.cell[class*='tag_collapse'] .collapse-toggle-bar",
+    );
+    
+    console.log(`Found ${collapsableCodeToggles.length} collapse toggles to fix`);
+    
+    // Remove existing event listeners by cloning and replacing elements
+    for (let i = 0; i < collapsableCodeToggles.length; i++) {
+      const oldToggle = collapsableCodeToggles[i];
+      const newToggle = oldToggle.cloneNode(true);
+      oldToggle.parentNode.replaceChild(newToggle, oldToggle);
+      
+      // Add improved event listener
+      newToggle.addEventListener("click", function (e) {
+        console.log('Collapse toggle clicked with improved behavior');
+        e.preventDefault();
+        var codeBlock = this.closest("div.cell[class*='tag_collapse']");
+        var codeBlockH = codeBlock.querySelector(".highlight");
+        var indicator = this.querySelector(".collapse-indicator");
+
+        if (codeBlock.classList.contains("expanded")) {
+          console.log('Collapsing code block...');
+          codeBlock.classList.remove("expanded");
+          indicator.textContent = "Expand";
+          
+          // Apply height based on collapse class
+          const collapseAccToHeight = (classList, elH) => {
+            for (let className of classList) {
+              if (className.startsWith("tag_collapse-")) {
+                const index = className.indexOf("-");
+                const height = className.substring(index + 1);
+                if (height && !isNaN(height)) {
+                  elH.style.height = parseInt(height) + 0.5 + "em";
+                  return true;
+                }
+              }
+            }
+            return false;
+          };
+          
+          collapseAccToHeight(codeBlock.classList, codeBlockH);
+          
+          // Improved scroll behavior for better reading continuity
+          setTimeout(() => {
+            console.log('Applying improved scroll positioning...');
+            const rect = codeBlock.getBoundingClientRect();
+            const viewportHeight = window.innerHeight;
+            
+            // Position the collapsed code block so the reader can continue reading
+            // Position the bottom of the collapsed block about 30% from the top of viewport
+            // This leaves about 70% of the viewport showing content below the collapsed block
+            const targetPositionFromTop = viewportHeight * 0.3;
+            const currentScrollTop = window.pageYOffset || document.documentElement.scrollTop;
+            const elementTop = rect.top + currentScrollTop;
+            const elementHeight = rect.height;
+            
+            // Calculate scroll position to put the bottom of collapsed block at target position
+            const newScrollTop = elementTop + elementHeight - targetPositionFromTop;
+            
+            // Ensure we don't scroll past page boundaries
+            const maxScrollTop = Math.max(0, document.documentElement.scrollHeight - viewportHeight);
+            const finalScrollTop = Math.max(0, Math.min(newScrollTop, maxScrollTop));
+            
+            console.log(`Scrolling to position ${finalScrollTop} for optimal reading flow`);
+            
+            window.scrollTo({
+              top: finalScrollTop,
+              behavior: 'smooth'
+            });
+          }, 150); // Slightly longer delay for height change to complete
+        } else {
+          console.log('Expanding code block...');
+          codeBlock.classList.add("expanded");
+          indicator.textContent = "Collapse";
+          codeBlockH.style.height = "auto";
+        }
+      });
+    }
+  }, 1500); // Wait for theme JS to fully load
+});