fix: Field allways passes a undefined className to custom component

.changeset/real-wolves-cough.md

@@ -0,0 +1,5 @@
+---
+'formik': patch
+---
+
+fix Field allways passes a undefined className to custom component

packages/formik/src/Field.tsx

@@ -22,19 +22,19 @@ export interface FieldConfig<V = any> {
    * Field component to render. Can either be a string like 'select' or a component.
    */
   component?:
-  | string
-  | React.ComponentType<FieldProps<V>>
-  | React.ComponentType
-  | React.ForwardRefExoticComponent<any>;
+    | string
+    | React.ComponentType<FieldProps<V>>
+    | React.ComponentType
+    | React.ForwardRefExoticComponent<any>;
 
   /**
    * Component to render. Can either be a string e.g. 'select', 'input', or 'textarea', or a component.
    */
   as?:
-  | React.ComponentType<FieldProps<V>['field']>
-  | string
-  | React.ComponentType
-  | React.ForwardRefExoticComponent<any>;
+    | React.ComponentType<FieldProps<V>['field']>
+    | string
+    | React.ComponentType
+    | React.ForwardRefExoticComponent<any>;
 
   /**
    * Render prop (works like React router's <Route render={props =>} />)
@@ -72,10 +72,12 @@ export interface FieldConfig<V = any> {
   innerRef?: (instance: any) => void;
 }
 
-export type FieldAttributes<T> = { className?: string; } & GenericFieldHTMLAttributes &
+export type FieldAttributes<T> = {
+  className?: string;
+} & GenericFieldHTMLAttributes &
   FieldConfig<T> &
   T & {
-    name: string,
+    name: string;
   };
 
 export type FieldHookConfig<T> = GenericFieldHTMLAttributes & FieldConfig<T>;
@@ -141,7 +143,6 @@ export function Field({
   children,
   as: is, // `as` is reserved in typescript lol
   component,
-  className,
   ...props
 }: FieldAttributes<any>) {
   const {
@@ -205,14 +206,14 @@ export function Field({
       const { innerRef, ...rest } = props;
       return React.createElement(
         component,
-        { ref: innerRef, ...field, ...rest, className },
+        { ref: innerRef, ...field, ...rest },
         children
       );
     }
     // We don't pass `meta` for backwards compat
     return React.createElement(
       component,
-      { field, form: formik, ...props, className },
+      { field, form: formik, ...props },
       children
     );
   }
@@ -224,10 +225,10 @@ export function Field({
     const { innerRef, ...rest } = props;
     return React.createElement(
       asElement,
-      { ref: innerRef, ...field, ...rest, className },
+      { ref: innerRef, ...field, ...rest },
       children
     );
   }
 
-  return React.createElement(asElement, { ...field, ...props, className }, children);
+  return React.createElement(asElement, { ...field, ...props }, children);
 }

packages/formik/test/Field.test.tsx

@@ -100,10 +100,14 @@ describe('Field / FastField', () => {
 
   describe('renders an <input /> by default', () => {
     it('<Field />', () => {
-      const className = 'field-custom'
-      const { container } = renderForm(<Field name="name" className={className} />);
+      const className = 'field-custom';
+      const { container } = renderForm(
+        <Field name="name" className={className} />
+      );
       expect(container.querySelectorAll('input')).toHaveLength(1);
-      expect(container.querySelector(`.${className}`)?.getAttribute('value')).toEqual('jared')
+      expect(
+        container.querySelector(`.${className}`)?.getAttribute('value')
+      ).toEqual('jared');
     });
 
     it('<FastField />', () => {
@@ -112,22 +116,6 @@ describe('Field / FastField', () => {
     });
   });
 
-  describe('renders an <input /> with className', () => {
-    it('<Field />', () => {
-      const className = 'field-custom'
-      const { container } = renderForm(<Field name="name" className={className} />);
-      expect(container.querySelectorAll(`.${className}`)).toHaveLength(1)
-      expect(container.querySelector(`.${className}`)?.getAttribute('value')).toEqual('jared')
-    });
-
-    it('<FastField />', () => {
-      const className = 'field-custom'
-      const { container } = renderForm(<FastField name="name" className={className} />);
-      expect(container.querySelectorAll(`.${className}`)).toHaveLength(1)
-      expect(container.querySelector(`.${className}`)?.getAttribute('value')).toEqual('jared')
-    });
-  });
-
   describe('receives { field, form, meta } props and renders element', () => {
     it('<Field />', () => {
       let injected: FieldProps[] = [];
@@ -222,7 +210,7 @@ describe('Field / FastField', () => {
   });
 
   describe('children', () => {
-    cases('renders a child element with component', () => {
+    it('renders a child element with component', () => {
       const { container } = renderForm(
         <Field name="name" component="select">
           <option value="Jared" label={TEXT} />
@@ -233,7 +221,7 @@ describe('Field / FastField', () => {
       expect(container.querySelectorAll('option')).toHaveLength(2);
     });
 
-    cases('renders a child element with as', () => {
+    it('renders a child element with as', () => {
       const { container } = renderForm(
         <Field name="name" as="select">
           <option value="Jared" label={TEXT} />
@@ -604,6 +592,48 @@ describe('Field / FastField', () => {
 
     expect(getProps().field.value).toBe('Binding');
   });
+
+  describe('renders an <input /> with className', () => {
+    it('<Field />', () => {
+      const className = 'field-custom';
+      const { container } = renderForm(
+        <Field name="name" className={className} />
+      );
+      expect(container.querySelectorAll(`.${className}`)).toHaveLength(1);
+      expect(
+        container.querySelector(`.${className}`)?.getAttribute('value')
+      ).toEqual('jared');
+    });
+
+    it('<FastField />', () => {
+      const className = 'field-custom';
+      const { container } = renderForm(
+        <FastField name="name" className={className} />
+      );
+      expect(container.querySelectorAll(`.${className}`)).toHaveLength(1);
+      expect(
+        container.querySelector(`.${className}`)?.getAttribute('value')
+      ).toEqual('jared');
+    });
+  });
+  cases(
+    "render custom component and doesn't overwrite className",
+    renderField => {
+      const { container } = renderField({
+        children: ({ form, field, ...reset }) => (
+          /**
+           *  @see https://github.com/jaredpalmer/formik/issues/3883
+           *  ensure when Field or FastField component don't review classNames,
+           *  they won't pass {className:undefined} to custom component
+           *
+           */
+          <input name="name" className="custom-class" {...reset} />
+        ),
+      });
+
+      expect(container.querySelector('.custom-class')).toBeTruthy();
+    }
+  );
 });
 
 // @todo Deprecated