30秒学会 React 片段 – LimitedTextarea

Renders a textarea component with a character limit.

• Use the React.useState() hook to create the content state variable and set its value to value.
  Create a method setFormattedContent, which trims the content of the input if it’s longer than limit.
• Use the React.useEffect() hook to call the setFormattedContent method on the value of the content state variable.
• Use a<div> to wrap both the<textarea> and the <p> element that displays the character count and bind the onChange event of the <textarea> to call setFormattedContent with the value of event.target.value.

代码实现

function LimitedTextarea({ rows, cols, value, limit }) {
  const [content, setContent] = React.useState(value);

  const setFormattedContent = text => {
    text.length > limit ? setContent(text.slice(0, limit)) : setContent(text);
  };

  React.useEffect(() => {
    setFormattedContent(content);
  }, []);

  return (
    <div>
      <textarea
        rows={rows}
        cols={cols}
        onChange={event => setFormattedContent(event.target.value)}
        value={content}
      />
      <p>
        {content.length}/{limit}
      </p>
    </div>
  );
}

使用样例

ReactDOM.render(<LimitedTextarea limit={32} value="Hello!" />, document.getElementById('root'));