fix(classname): support mix via valueOf method

Author: Nikita Stenin

packages/classname/classname.ts

@@ -92,9 +92,9 @@ export function withNaming(preset: Preset): ClassNameInitilizer {
         const value = mix[i]
 
         // Skipping non-string values and empty strings
-        if (typeof value !== 'string' || !value) continue
+        if (!value || typeof value.valueOf() !== 'string') continue
 
-        const mixes = value.split(' ')
+        const mixes = value.valueOf().split(' ')
 
         for (let j = 0; j < mixes.length; j++) {
           const val = mixes[j]

packages/classname/test/classname.test.ts

@@ -128,6 +128,11 @@ describe('@bem-react/classname', () => {
           'Block-Elem Block-Elem_theme_normal Block-Elem_size_m',
         )
       })
+
+      test('object with valueOf', () => {
+        const b = cn('Block')
+        expect(b('Elem', null, [{ valueOf: () => 'Mix' } as string])).toEqual('Block-Elem Mix')
+      })
     })
   })