React之Froms

In React, a <textarea> uses a value attribute instead. This way, a form using a <textarea>can be written very similarly to a form that uses a single-line input:

React中    使用value属性显示区域内容。

<textarea value={this.state.value} onChange={this.handleChange} />

Note that the Coconut option is initially selected, because of the selected attribute. React, instead of using this selected attribute, uses a value attribute on the root select tag. This is more convenient in a controlled component because you only need to update it in one place. For example:

hmtl和react中使用select的区别

html中使用子元素中的selected属性标注

<select>
  <option value="grapefruit">Grapefruit</option>
  <option value="lime">Lime</option>
  <option selected value="coconut">Coconut</option>
  <option value="mango">Mango</option>
</select>

react中在父元素中加入value，然后在通过change时间，修改state中的value，

class FlavorForm extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: 'coconut'};
 
    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }
 
  handleChange(event) {
    this.setState({value: event.target.value});
  }
 
  handleSubmit(event) {
    alert('Your favorite flavor is: ' + this.state.value);
    event.preventDefault();
  }
 
  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label>
          Pick your favorite La Croix flavor:
          <select value={this.state.value} onChange={this.handleChange}>
            <option value="grapefruit">Grapefruit</option>
            <option value="lime">Lime</option>
            <option value="coconut">Coconut</option>
            <option value="mango">Mango</option>
          </select>
        </label>
        <input type="submit" value="Submit" />
      </form>
    );
  }
}

如此一来，react中对input/select、textarea的取值统一为取value属性的值