Move the validation to main()

demos/hello-three/demo.js

 
 (function() {
 
-// Validate
-if(typeof encantar === 'undefined')
-    throw new Error(`Can't find the three.js plugin for encantar.js`);
-
-
-
 /**
  * Utilities for the Demo scene
  */
     }
 }
 
-
-
 /**
  * Demo scene
  */
     }
 }
 
-
-
 /**
  * Enchant the scene
  * @returns {void}
 {
     const scene = new DemoScene();
 
+    if(typeof encantar === 'undefined')
+        throw new Error(`Can't find the three.js plugin for encantar.js`);
+
     encantar(scene).catch(error => {
         alert(error.message);
     });