reverted partial client side back button logic, but also now tested / validated if somehow we are in a flat view and ask for entries and dont get all of them back, or we are in folder view and we try to go into a folder or back up a folder and we get no data as someone deleted it since we made the view, so then show appropriate client-side errors

internal/js/files_support.js

@@ -449,6 +449,11 @@ function getDirEntries(dir_id, back)
         contentType: 'application/json',
         dataType: 'json',
         success: function(res) {
+            if( res.valid === false )
+            {
+                $('#figures').html( "<alert class='alert alert-danger'>ERROR! directory has changed since you loaded this view.  You have to reload and reset your view (probably someone deleted the directory or its parent since you loaded this page)" )
+                return
+            }
             entryList=res.entry_list
             pageList=entryList.slice(0, OPT.how_many)
             // now go get actual data/entries
@@ -468,6 +473,10 @@ function drawPageOfFigures()
     var last = { printed: null }
     var ecnt=0
 
+    // something is up, let the user know
+    if( document.alert )
+        $('#figures').append( document.alert )
+
     if( OPT.folders )
     {
         // it root_eid is 0, then no entries in this path - cant go up
@@ -476,18 +485,23 @@ function drawPageOfFigures()
             gray="_gray"
             back=""
             cl=""
+            back_id=0
         }
         else
         {
             gray=""
             back="Back"
             cl="back"
+            if( document.entries.length > 0 )
+                back_id = document.entries[0].in_dir.eid
+            else
+                back_id = document.back_id
         }
         // back button, if gray/back decide if we see grayed out folder and/or the name of the folder we go back to
         // with clas "back" this gets a different click handler which flags server to return data by 'going back/up' in dir tree
         // we give the server the id of the first item on the page so it can work out how to go back
         html=`<div class="col col-auto g-0 m-1">
-                <figure id="${document.entries[0].id}" ecnt="0" class="${cl} entry m-1" type="Directory">
+                <figure id="${back_id}" ecnt="0" class="${cl} entry m-1" type="Directory">
                     <svg class="svg" width="${OPT.size-22}" height="${OPT.size-22}">
                         <use xlink:href="internal/icons.svg#folder_back${gray}"/>
                     </svg>
@@ -517,6 +531,11 @@ function drawPageOfFigures()
 function getPageFileList(res, viewingIdx)
 {
     $('#file_list_div').empty()
+
+    // something is up, let the user know
+    if( document.alert )
+        $('#file_list_div').append( '<div class="row">' + document.alert + '</div>' )
+
     if( OPT.root_eid == 0 )
     {
         $('#file_list_div').append( `<span class="alert alert-danger p-2">No files in Path!</span>` )
@@ -558,11 +577,17 @@ function getPage(pageNumber, successCallback, viewingIdx=0)
     data={}
     data.ids = pageList
 
+    // assume nothing wrong, but if the data goes odd, then this will be non-null and displayed later (cant add here, as later code does .empty() of file divs)
+    document.alert=null
+
     $.ajax({
         type: 'POST', url: '/get_entries_by_ids',
         data: JSON.stringify(data), contentType: 'application/json',
         dataType: 'json',
         success: function(res) { 
+            if( res.length != pageList.length )
+                document.alert="<alert class='alert alert-warning'>WARNING: something in data has changed since viewing this page (likely someone deleted content in another view), strongly suggest a page reload to get the latest data</alert>"
+            
             document.entries=res;
             successCallback(res,viewingIdx)
             resetNextPrevButtons()