import React from "react";
import { Formik, Form, Field } from "formik";

function validateEmail(value) {
  let error;
  
  if (!value) {
    error = "Required";
  } else if (!/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i.test(value)) {
    error = "Invalid email address";
  }
  
  return error;
}

function validateUsername(value) {
  let error;
  
  if (value === "admin") {
    error = "Nice try!";
  }
  
  return error;
}

const Example = () => {
  const onSubmit = values => {
    console.log(values);
  };

  return (
    <Formik
      initialValues={{
        username: "",
        email: ""
      }}
      onSubmit={onSubmit}
    >
      {({ errors, touched }) => (
        <Form>
          <Field name="email" validate={validateEmail} />
          {errors.email && touched.email && errors.email}

          <Field name="username" validate={validateUsername} />
          {errors.username && touched.username && errors.username}

          <button type="submit">Submit</button>
        </Form>
      )}
    </Formik>
  );
};

import React from "react";
import { useForm } from "react-hook-form";

const Example = () => {
  const { handleSubmit, register, errors } = useForm();
  const onSubmit = values => {
    console.log(values);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input
        name="email"
        ref={register({
          required: 'Required',
          pattern: {
            value: /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i,
            message: "invalid email address"
          }
        })}
      />
      {errors.email && errors.email.message}

      <input
        name="username"
        ref={register({
          validate: value => value !== "admin" || "Nice try!"
        })}
      />
      {errors.username && errors.username.message}

      <button type="submit">Submit</button>
    </form>
  );
};

import React from "react";
import { Provider } from "react-redux";
import { Field, reduxForm } from "redux-form";
import store from "./store";

const validate = values => {
  const errors = {};

  if (!values.username) {
    errors.username = "Required";
  } else if (values.username === "admin") {
    errors.username = "Nice try!";
  }

  if (!/^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i.test(values.email)) {
    errors.email = "Invalid email address";
  }

  return errors;
};

const renderField = ({ input, label, type, meta: { touched, error } }) => (
  <>
    <input {...input} placeholder={label} type={type} />
    {touched && error && <span>{error}</span>}
  </>
);

const Form = props => {
  const { handleSubmit } = props;
  const onSubmit = values => {
    console.log(values);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <Field name="email" type="email" component={renderField} label="Email" />
      <Field name="username" component={renderField} label="Username" />
    
      <button type="submit">Submit</button>
    </form>
  );
};

const FormRedux = reduxForm({ form: "syncValidation", validate })(Form);

const Example = () => (
  <Provider store={store}>
    <FormRedux />
  </Provider>
);