fix: Turtle.js.get/set_heading returned NaN ( fixes: #334, fixes: #336, fixes: #337, fixes: #338 )

Author: ninmonkey

Types/Turtle.js/get_heading.js

@@ -0,0 +1,7 @@
+function get_heading() {
+    const _ = this
+    if ( _['#heading'] === undefined ) {
+        _['#heading'] = 0.0
+    }
+    return _['#heading']
+}

Types/Turtle.js/heading.js

@@ -1,11 +1,9 @@
 function set_heading(value) {
-    let _ = this
+    const _ = this
     try {
         _['#heading'] = new Number(value)
     } catch {
-        
         _['#heading'] = 0.0
     }
-    
     return _
 }