Add TargetType enum for use by/with extensions

src/extension-support/extension-worker.js

@@ -3,6 +3,7 @@
 const ArgumentType = require('../extension-support/argument-type');
 const BlockType = require('../extension-support/block-type');
 const dispatch = require('../dispatch/worker-dispatch');
+const TargetType = require('../extension-support/target-type');
 
 class ExtensionWorker {
     constructor () {
@@ -47,6 +48,7 @@ class ExtensionWorker {
 global.Scratch = global.Scratch || {};
 global.Scratch.ArgumentType = ArgumentType;
 global.Scratch.BlockType = BlockType;
+global.Scratch.TargetType = TargetType;
 
 /**
  * Expose only specific parts of the worker to extensions.

src/extension-support/target-type.js

@@ -0,0 +1,17 @@
+/**
+ * Default types of Target supported by the VM
+ * @enum {string}
+ */
+const TargetType = {
+    /**
+     * Rendered target which can move, change costumes, etc.
+     */
+    SPRITE: 'sprite',
+
+    /**
+     * Rendered target which cannot move but can change backdrops
+     */
+    STAGE: 'stage'
+};
+
+module.exports = TargetType;