remember state of folds

index.html

@@ -104,7 +104,7 @@ function make_head(c,index="") {
     var name=c.substring(1).trim();
     var head=c.replace(/ /g," ");
     var id=name.replace(/ /g,"")+"_"+index;
-    return '<a name="'+name+'" id="anchor_'+id+'" onclick="fold_content(\''+id+'\')">'+
+    return '<a name="'+name+'" id="anchor_'+id+'" onclick="fold_toggle(\''+id+'\')">'+
         '<div class=head align=center id="head_'+id+'">'+head+'</div></a>'+
         '<hr WIDTH="100%" SIZE=3 NOSHADE>';
 }
@@ -354,29 +354,79 @@ function filter_cookies(cookies,name) {
       }
     }
   }
-  return null
+  return null;
 }
-function fold_content(name) {
+function fold_toggle(name,save_state = true) {
   if (!narrow_window()) { return }
   if (!config.foldCategories) { return }
   var title = document.getElementById("head_"+name);
   var el = document.getElementById("content_"+name);
   el.hidden = ! el.hidden;
   title.classList.toggle("fold_plus");
+  if (save_state) {
+    set_cookie("fold",fold_get_state());
+  }
+}
+function fold_set(name,value) {
+  if (!narrow_window()) { return }
+  if (!config.foldCategories) { return }
+  var title = document.getElementById("head_"+name);
+  var el = document.getElementById("content_"+name);
+  el.hidden = value;
+  if (value) {
+    title.classList.add("fold_plus");
+  } else {
+    title.classList.remove("fold_plus");
+  }
 }
 function fold_initial() {
   if (!narrow_window()) { return }
   if (!config.foldCategories) { return }
+  var state = get_cookie("fold");
+  if (state !== null) {
+    fold_set_state(state);
+    return;
+  }
   var slides = document.getElementsByClassName("head");
   for(var i = 0; i < slides.length; i++) {
     var el = slides.item(i);
     var rect = el.getBoundingClientRect();
     if (window.innerHeight*1.5 < rect.top) {
       var name = el.id.replace("head_","");
-      fold_content(name);
+      fold_toggle(name);
     }
   }
 }
+function fold_get_state() {
+  var slides = document.getElementsByClassName("head");
+  var state = "";
+  for(var i = 0; i < slides.length; i++) {
+    var title = slides.item(i);
+    var name = title.id.replace("head_","");
+    var el = document.getElementById("content_"+name);
+    if (el.hidden) {
+      state += '-';
+    } else {
+      state += '+';
+    }
+  }
+  return state;
+}
+function fold_set_state(state) {
+  var slides = document.getElementsByClassName("head");
+  for(var i = 0; i < slides.length; i++) {
+    var title = slides.item(i);
+    var name = title.id.replace("head_","");
+    if (state[i] == '-') {
+      fold_set(name, true);
+    }
+    if (state[i] == '+') {
+      fold_set(name, false);
+    }
+  }
+  return;
+}
+
 function set_cookie(name,value) {
   // Save cookies for 2 hours
   document.cookie = name + "=" + value.toString() + "&" + window.location.pathname +