Merge pull request #1709 from mzgoddard/cast-to-number

Shortcut Cast.toNumber if given a number

src/util/cast.js

@@ -1,5 +1,13 @@
 const Color = require('../util/color');
 
+/**
+ * Store and possibly polyfill Number.isNaN. Number.isNaN can save time over
+ * self.isNaN by not coercing its input. We need to polyfill it to support
+ * Internet Explorer.
+ * @const
+ */
+const _NumberIsNaN = Number.isNaN || isNaN;
+
 /**
  * @fileoverview
  * Utilities for casting and comparing Scratch data-types.
@@ -20,8 +28,19 @@ class Cast {
      * @return {number} The Scratch-casted number value.
      */
     static toNumber (value) {
+        // If value is already a number we don't need to coerce it with
+        // Number().
+        if (typeof value === 'number') {
+            // Scratch treats NaN as 0, when needed as a number.
+            // E.g., 0 + NaN -> 0.
+            if (_NumberIsNaN(value)) {
+                return 0;
+            }
+            return value;
+        }
+
         const n = Number(value);
-        if (isNaN(n)) {
+        if (_NumberIsNaN(n)) {
             // Scratch treats NaN as 0, when needed as a number.
             // E.g., 0 + NaN -> 0.
             return 0;