30秒学会 React 片段 – LimitedWordTextarea

Renders a textarea component with a word limit.

• Use the React.useState() hook to create the content and wordCount state variables and set their values to value and 0 respectively.
• Create a method setFormattedContent, which uses String.prototype.split(' ') to turn the input into an array of words and check if the result of applying Array.prototype.filter(Boolean) has a length longer than limit.
• If the afforementioned length exceeds the limit, trim the input, otherwise return the raw input, updating content and wordCount accordingly in both cases.
• 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 LimitedWordTextarea({ rows, cols, value, limit }) {
  const [content, setContent] = React.useState(value);
  const [wordCount, setWordCount] = React.useState(0);

  const setFormattedContent = text => {
    let words = text.split(' ');
    if (words.filter(Boolean).length > limit) {
      setContent(
        text
          .split(' ')
          .slice(0, limit)
          .join(' ')
      );
      setWordCount(limit);
    } else {
      setContent(text);
      setWordCount(words.filter(Boolean).length);
    }
  };

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

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

使用样例

ReactDOM.render(
  <LimitedWordTextarea limit={5} value="Hello there!" />,
  document.getElementById('root')
);