Started working on migration logic

migrations.js

@@ -0,0 +1,32 @@
+// bumps save versions
+
+migrations = [
+  // 0 -> 1
+  // notes: only adds version number
+  function(save) {
+    save["version"] = 1;
+  }
+  //
+]
+
+function migrate(save, target=null) {
+  if (target == null) {
+    target = migrations.length;
+  }
+
+  let version = save.version;
+
+  if (version == undefined) {
+    version = 0;
+  }
+
+  if (version < target) {
+    for (let x = version; x < target; x++) {
+      migrations[x](save);
+    }
+  } else {
+    return false;
+  }
+
+  return true;
+}

stroll.html

@@ -6,6 +6,7 @@
   <title>Stroll</title>
   <link rel="stylesheet" href="style.css">
   <script src="sounds.js"></script>
+  <script src="migrations.js"></script>
   <script src="presets.js"></script>
   <script src="units.js"></script>
   <script src="recursive-macro.js"></script>
@@ -371,7 +372,7 @@
     <p>Lengths in meters, areas in square meters, masses in kilograms, times in seconds</p>
     <p>(but you can preview the customary value)</p>
     <p>Click on boxed titles to enable and disable features.</p>
-    
+
     <div id="custom-species">