fix(front, back) -> undefined exception; feat(resize)

src/utils/concept.js

@@ -31,4 +31,4 @@ export function satisfiesConcept(obj, pure_virtual, virtual, debug) {
     }
   }
   return true
-}
+}

src/utils/mixin.js

@@ -4,4 +4,4 @@ export function mixinClasses(dest, ...sources) {
     delete properties.constructor
     Object.defineProperties(dest.prototype, properties)
   }
-}
+}