deal with requirements defined before init

README.md

@@ -17,7 +17,7 @@ In order to defer your scripts, you need to replace in your `PageController` the
     {
         parent::init();
 
-        Requirements::set_backend(new DeferBackend);
+        DeferBackend::replaceBackend();
     }
 
 Once this is done, all scripts (provided by modules or yourself) will be deferred. This is great

src/DeferBackend.php

@@ -32,6 +32,32 @@ public static function getDeferBackend()
         return $backend;
     }
 
+    /**
+     * @param Requirements_Backend $oldBackend defaults to current backend
+     * @return $this
+     */
+    public static function replaceBackend(Requirements_Backend $oldBackend = null)
+    {
+        if ($oldBackend === null) {
+            $oldBackend = Requirements::backend();
+        }
+        $deferBackend = new static;
+        foreach ($oldBackend->getCSS() as $file => $opts) {
+            $deferBackend->css($file, null, $opts);
+        }
+        foreach ($oldBackend->getJavascript() as $file => $opts) {
+            $deferBackend->javascript($file, null, $opts);
+        }
+        foreach ($oldBackend->getCustomCSS() as $id => $script) {
+            $deferBackend->customCSS($script, $id);
+        }
+        foreach ($oldBackend->getCustomScripts() as $id => $script) {
+            $deferBackend->customScript($script, $id);
+        }
+        Requirements::set_backend($deferBackend);
+        return $deferBackend;
+    }
+
     /**
      * @inheritDoc
      */