30秒学会 React 片段 – usePrevious

A hook that stores the previous state or props.

• Create a custom hook that takes a value.
• Use the React.useRef() hook to create a ref for the value.
• Use the React.useEffect() hook to remember the latest value.

代码实现

const usePrevious = value => {
  const ref = React.useRef();
  React.useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}

使用样例

const Counter = () => {
  const [value, setValue] = React.useState(0);
  const lastValue = usePrevious(value);

  return (
    <div>
      <p>Current: {value} - Previous: {lastValue}</p>
      <button onClick={() => setValue(value + 1)}>Increment</button>
    </div>
  );
};

ReactDOM.render(<Counter />, document.getElementById('root'));