问如何使用reactjs验证我的表单元素？

EN

import React, { useState } from 'react';
import PropTypes from 'prop-types';

function MyComponent() {
  const initialState = {
    userName: '',
    password: '',
    error: ''
  }

  const [values, setValues] = useState(initialState);

  const handleInputChange = event => {
    const { name, value } = event.target;

    setValues({ ...values, [name]: value.trim() });
  };

  const handleSubmit = event => {
    event.preventDefault();

    if (values.userName.length === 0 || values.password.length === 0) {
      setValues({ ...values, error: "Please fill this field" });
    }
    else {
      setValues({ ...values, error: "" });
    }

    // Handle form submission
    console.log("formData", values);
  };

  return (
    //call handleInputChange on state change event
    //call handleSubmit on onSubmit event
    //display the div containing the error and apply the error class
    <form onSubmit={handleSubmit}>
      {values.error && <div>{values.error}</div>}

      <input type='text' name='userName' placeholder="User Name" value={values.userName || ''} onChange={handleInputChange} />
      <input type='password' name='password' placeholder="Password" value={values.password || ''} onChange={handleInputChange} />
      <button type="submit">Submit</button>
    </form>
  )
}

MyComponent.propTypes = {
  userName: PropTypes.string.isRequired,
  password: PropTypes.string.isRequired,
  error: PropTypes.string.isRequired
};

export default MyComponent;

import React from 'react';
import './style.scss';

class MyComponent extends React.Component {
  // initial state
state = {
   username : { val: "", err : "" },
   // ... etc
}

handleInputChange (e)   {
  // your logic for input change
  // you can even including "pre-validation" in this step
  const val = e.target.value;
  this.setState({ username: { val, err: "" } })
}

handleSubmit = () => {
   const { username, password } = this.state
   // better to validate password and login with some library, this is just an example
   // you should reset value of input on error and 
   // add `err`..err should be handled in your template where it should be shown
   if ( !username.length ) this.setState({ username: { val: "", err: "Please fill this field" } })

   //...submit stuff

}

render = () => {
  return ( // your template )
}