获取TypeError:在ReactJs上未定义this.props

Question

我正在尝试做教程:https://facebook.github.io/react/docs/tutorial.html

import React, { PropTypes } from 'react';
import classnames from 'classnames';
import styles from './CommentBox.css';
import withStyles from '../../decorators/withStyles';
import Link from '../../utils/Link';
import $ from 'jquery';

@withStyles(styles)
class CommentBox extends React.Component {

    constructor() {
        super();
        this.state = {data: []};
    }

    loadCommentsFromServer() {
        $.ajax({
            url: this.props.url,
            dataType: 'json',
            cache: false,
            success: function(data) {
                this.setState({data: data});
            }.bind(this),
            error: function(xhr, status, err) {
                console.error(this.props.url, status, err.toString());
            }.bind(this)
        })
    }

    componentDidMount() {
        this.loadCommentsFromServer();
        setInterval(this.loadCommentsFromServer, this.props.pollInterval);
    }

    render() {

        let url="/public/comments.json"

        return (
            <div className="commentBox">
                <h1>Comments</h1>
                <CommentList data={this.state.data} />
                <CommentForm />
            </div>
        );
    }

}

class CommentList extends React.Component {

    render() {

        let data = this.props.data

        var commentNodes = data.map(function (comment) {
          return (
            <Comment author={comment.author}>
              {comment.text}
            </Comment>
          );
        });

        return (
          <div className="commentList">
            {commentNodes}
          </div>
        );
    }
};

class Comment extends React.Component {
    render() {
        return(
            <div className="comment">
            <h2 className="commentAuthor">
              {this.props.author}
            </h2>
            {this.props.children}
          </div>
        );
    }
}

class CommentForm extends React.Component {
  render() {
    return (
      <div className="commentForm">
        Hello, world! I am a CommentForm.
      </div>
    );
  }
};

export default CommentBox;

但是,该教程有点过时,我使用React 0.14-rc1和ES6语法.我已尽力遵循教程并以0.14方式实现它.能够达到这一点,但现在得到错误:

TypeError: this.props is undefined

无法弄清楚这个问题.知道为什么吗？谢谢

Answer 1

使用React和ES6类时, React不会自动绑定在类上声明的函数.

因此,使用this.loadCommentsFromServer.bind(this)或使用箭头功能

loadCommentsFromServer = () => {}

Answer 2

随着React从createClass的转移,ES6 classes我们需要自己处理this我们方法的正确值,如下所述:http://www.newmediacampaigns.com/blog/refactoring-react-components-to-es6-classes 更改您的代码,使方法有限,以便在consructor中更正此值:

export default class ComponentClass extends React.Component {
  constructor(props) {
      super(props);
      this._myHandler = this._myHandler.bind(this);
  }

  _myHandler(props) {
    console.log(props);
  }

  render() {
    return (
        <div className="col-xs-6 col-md-4">
            <button type="button" className="btn btn-danger" onClick={this._myHandler}><i className="fa fa-trash"> Delete</i></button>
        </div>
    )
  }
}

这no autobinding是来自React家伙为ES6课程的刻意步骤.提供了自动绑定到正确的上下文React.createClass.有关详细信息,请访问:https://facebook.github.io/react/blog/2015/01/27/react-v0.13.0-beta-1.html#autobinding

因此,基于此,您还可以将代码更改为:

export default class ComponentClass extends React.Component {
  _myHandler = (props) => {
    console.log(props);
  }

  render() {
    return (
        <div className="col-xs-6 col-md-4">
            <button type="button" className="btn btn-danger" onClick={this._myHandler}><i className="fa fa-trash"> Delete</i></button>
        </div>
    )
  }
}

Answer 3

将传递props给构造函数将有所帮助：

constructor(props) {
    super(props);
}