Clarify need of parameters in addClassesToSVGElement. Resolves #479

plugins/addClassesToSVGElement.js

@@ -6,18 +6,41 @@ exports.active = false;
 
 exports.description = 'adds classnames to an outer <svg> element';
 
+var ENOCLS = 'Error in plugin "addClassesToSVGElement": absent parameters.\n\
+It should have a list of classes in "classNames" or one "className".\n\
+Config example:\n\n\
+\
+plugins:\n\
+- addClassesToSVGElement:\n\
+    className: "mySvg"\n\n\
+\
+plugins:\n\
+- addClassesToSVGElement:\n\
+    classNames: ["mySvg", "size-big"]\n';
+
 /**
- * Add classnames to an outer <svg> element.
+ * Add classnames to an outer <svg> element. Example config:
+ *
+ * plugins:
+ * - addClassesToSVGElement:
+ *     className: 'mySvg'
+ *
+ * plugins:
+ * - addClassesToSVGElement:
+ *     classNames: ['mySvg', 'size-big']
  *
  * @author April Arcus
  */
 exports.fn = function(data, params) {
+    if (!params || !(Array.isArray(params.classNames) && params.classNames.some(String) || params.className)) {
+        console.error(ENOCLS);
+        return data;
+    }
 
-    var classNames = params.classNames || [ params.className ];
+    var classNames = params.classNames || [ params.className ],
-    var svg = data.content[0];
+        svg = data.content[0];
 
     if (svg.isElem('svg')) {
-
         if (svg.hasAttr('class')) {
             svg.attr('class').value =
                 svg.attr('class').value
@@ -32,7 +55,6 @@ exports.fn = function(data, params) {
                 local: 'class'
             });
         }
-
     }
 
     return data;