Dynamic menus for costumes and backdrops

src/lib/blocks.js

 const ScratchBlocks = require('scratch-blocks');
 
 module.exports = function (vm) {
+
+    const jsonForMenuBlock = function (name, menuOptionsFn, colors) {
+        return {
+            message0: '%1',
+            args0: [
+                {
+                    type: 'field_dropdown',
+                    name: name,
+                    options: menuOptionsFn
+                }
+            ],
+            inputsInline: true,
+            output: 'String',
+            colour: colors.secondary,
+            colourSecondary: colors.secondary,
+            colourTertiary: colors.tertiary,
+            outputShape: ScratchBlocks.OUTPUT_SHAPE_ROUND
+        };
+    };
+
+    const soundsMenu = function () {
+        return vm.editingTarget.sprite.sounds.map(sound => [sound.name, sound.name]);
+    };
+
+    const costumesMenu = function () {
+        return vm.editingTarget.sprite.costumes.map(costume => [costume.name, costume.name]);
+    };
+
+    const backdropsMenu = function () {
+        return vm.runtime.targets[0].sprite.costumes.map(costume => [costume.name, costume.name]);
+    };
+
+    const soundColors = ScratchBlocks.Colours.sounds;
+
+    const looksColors = ScratchBlocks.Colours.looks;
+
     ScratchBlocks.Blocks.sound_sounds_menu.init = function () {
-        this.jsonInit(
-            {
-                message0: '%1',
-                args0: [
-                    {
-                        type: 'field_dropdown',
-                        name: 'SOUND_MENU',
-                        options: function () {
-                            const menu = vm.editingTarget.sprite.sounds.map(sound => [sound.name, sound.name]);
-                            return menu;
-                        }
-                    }
-                ],
-                inputsInline: true,
-                output: 'String',
-                colour: ScratchBlocks.Colours.sounds.secondary,
-                colourSecondary: ScratchBlocks.Colours.sounds.secondary,
-                colourTertiary: ScratchBlocks.Colours.sounds.tertiary,
-                outputShape: ScratchBlocks.OUTPUT_SHAPE_ROUND
-            });
+        const json = jsonForMenuBlock('SOUND_MENU', soundsMenu, soundColors);
+        this.jsonInit(json);
+    };
+
+    ScratchBlocks.Blocks.looks_costume.init = function () {
+        const json = jsonForMenuBlock('COSTUME', costumesMenu, looksColors);
+        this.jsonInit(json);
+    };
+
+    ScratchBlocks.Blocks.looks_backdrops.init = function () {
+        const json = jsonForMenuBlock('BACKDROP', backdropsMenu, looksColors);
+        this.jsonInit(json);
     };
+
     return ScratchBlocks;
 };