Fix Mouse.postData error if called before project loads

Author: GarboMuffin

src/io/mouse.js

@@ -101,16 +101,19 @@ class Mouse {
             if (!(data.x > 0 && data.x < data.canvasWidth &&
                 data.y > 0 && data.y < data.canvasHeight)) return;
 
+            // target will not exist if project is still loading
             const target = this._pickTarget(data.x, data.y);
-            const isNewMouseDown = !previousDownState && this._isDown;
-            const isNewMouseUp = previousDownState && !this._isDown;
-
-            // Draggable targets start click hats on mouse up.
-            // Non-draggable targets start click hats on mouse down.
-            if (target.draggable && isNewMouseUp) {
-                this._activateClickHats(target);
-            } else if (!target.draggable && isNewMouseDown) {
-                this._activateClickHats(target);
+            if (target) {
+                const isNewMouseDown = !previousDownState && this._isDown;
+                const isNewMouseUp = previousDownState && !this._isDown;
+
+                // Draggable targets start click hats on mouse up.
+                // Non-draggable targets start click hats on mouse down.
+                if (target.draggable && isNewMouseUp) {
+                    this._activateClickHats(target);
+                } else if (!target.draggable && isNewMouseDown) {
+                    this._activateClickHats(target);
+                }
             }
         }
     }

test/unit/tw_mouse.js

@@ -0,0 +1,14 @@
+const {test} = require('tap');
+const Runtime = require('../../src/engine/runtime');
+
+test('isDown does not error before project loads', t => {
+    const rt = new Runtime();
+    rt.ioDevices.mouse.postData({
+        isDown: true,
+        x: 20,
+        y: 20,
+        canvasWidth: 100,
+        canvasHeight: 100
+    });
+    t.end();
+});