React Hooks - 幕后发生了什么

React Hooks - 幕后发生了什么？

javascript
import React, { useState } from 'react';
function Counter() {
  const [count, setCount] = useState(0);
  const increment = () => {
    setCount(count + 1);
  };
  return (
    
      
Count: {count}
      Increment
    
  );
}

javascript
import React, { useState, useEffect } from 'react';
function Timer() {
  const [time, setTime] = useState(new Date());
  useEffect(() => {
    const timer = setInterval(() => {
      setTime(new Date());
    }, 1000);
    return () => {
      clearInterval(timer);
    };
  }, []);
  return (
    
      
Current Time: {time.toLocaleTimeString()}
    
  );
}

javascript
import React, { useState } from 'react';
function useInput(initialValue) {
  const [value, setValue] = useState(initialValue);
  const handleChange = (event) => {
    setValue(event.target.value);
  };
  return [value, handleChange];
}
function Form() {
  const [name, handleNameChange] = useInput('');
  const [email, handleEmailChange] = useInput('');
  return (
    
      
      
    
  );
}