JSONLoader: Helpful error when file is using new format. Fixes #5936.

src/loaders/JSONLoader.js

@@ -12,7 +12,7 @@ THREE.JSONLoader = function ( showStatus ) {
 };
 
 THREE.JSONLoader.prototype = Object.create( THREE.Loader.prototype );
-THREE.JSONLoader.prototype.constructor = THREE.JSONLoader;
+THREE.JSONLoader.prototype.constructor = THREE.JSONLoader;
 
 THREE.JSONLoader.prototype.load = function ( url, callback, texturePath ) {
 
@@ -43,6 +43,13 @@ THREE.JSONLoader.prototype.loadAjaxJSON = function ( context, url, callback, tex
 
 					var json = JSON.parse( xhr.responseText );
 
+					if ( json.metadata !== undefined && json.metadata.version >= 4 ) {
+
+						console.error( 'THREE.JSONLoader: "' + url + '" should be loaded with THREE.ObjectLoader instead.' );
+						return;
+
+					}
+
 					if ( json.metadata !== undefined && json.metadata.type === 'scene' ) {
 
 						console.error( 'THREE.JSONLoader: "' + url + '" seems to be a Scene. Use THREE.SceneLoader instead.' );