React.js如何使用getElementById方法获取道具中的ID？

Question

start to learn React.js recently and encounter the following problem: enter image description here

I want to get the div element using getElementById but it doesn't work and the console alerts can not read property 'props' of null . So how can I get the div element? it has troubled me for several hours. Thanks.

Answer 1

The whole idea with React is that you don't access the DOM, but work with a virtual DOM.

To achieve what you are trying to accomplish (which is a little unclear since the code is incomplete), you'll want to use a stateful component that stores user input on this.state . Check out this page on React forms.

You'll want to do something like this, where you are tracking user input by storing it on the component:

class NameForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: ''};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    alert('A name was submitted: ' + this.state.value);
    event.preventDefault();
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Name:
          <input type="text" value={this.state.value} onChange={this.handleChange} />
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}