MAGETWO-38867: Create mixin for declarative widget description

Author: Ihor Melnychenko

lib/web/mage/apply/scripts.js

@@ -32,9 +32,25 @@ define([
      * @param {HTMLElement} elem - Element whose data should be modified.
      */
     function setData(components, elem) {
-        var data = elem.getAttribute(dataAttr);
+        var data = elem.getAttribute(dataAttr),
+            iterator;
 
         data = !!data ? JSON.parse(data) : {};
+
+        if(components.mixins) {
+            data.mixins = data.mixins || {};
+
+            for(iterator in components.mixins){
+                if(!data.mixins[iterator]) {
+                    data.mixins[iterator] = components.mixins[iterator].slice();
+                }else {
+                    data.mixins[iterator] = data.mixins[iterator].concat(components.mixins[iterator]);
+                }
+            }
+
+            delete components.mixins;
+        }
+
         data = $.extend(true, data, components);
         data = JSON.stringify(data);