反应负载值并允许用户更改组件内的值

Question

I'm new to React (16.4.2), and I'm trying to understand the way it works. I don't want to complicate things with redux ; I just want to know about the core react library.

I have an application, and (eventually down the children chain) there is an input , which is a component, RangeInput . It's just a wrapper component for an input.

The problem is two parts

1. I should be able to change the value within the range (as a user)
2. if there is data in the local storage, it should load it the first time. This also means that the user should still be able to alter/change the input value.

Right now with this, I see to only be able to do one of the other. I know I'm not understanding something here.

What needs to happen?

Thanks, Kelly

Here are the classes:

export class RangeInput extends React.Component {
    constructor(props) {
       super(props);
       this.ds = new DataStore();
       this.state = {
          value: props.value
       };
    }

    static getDerivedStateFromProps(props, state) {
        console.log('props', props, 'state', state);
        if (props.value !== state.value) {
          return {value: props.value};
        }

        return null;
    }

    onChange(event) {
      const target = event.target;

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

      if (this.props.onChange) {
        this.props.onChange({value: target.value});
      }
   }

   onKeyUp(event) {
      if (event.keyCode !== 9) {
        return;
      }

      const target = event.target;

      if (this.props.onChange) {
        this.props.onChange({value: target.value});
      }
  }

  render() {
       return <div>
           <input type="number" value={this.state.value}
           onChange={this.onChange.bind(this)}
           onKeyUp={this.onKeyUp.bind(this)}/>
       </div>;
    }
}

const DATA_LOAD = 'load';
export class Application extends React.Component {
    constructor() {
       super();

       this.state = {
          value: -1,
          load = DATA_LOAD
       };
    }

    componentDidMount() {
      if (this.state.load === DATA_LOAD) {
         this.state.load = DATA_CLEAN;
         const eco = this.ds.getObject('the-app');
         if (eco) {
            this.setState({value: eco});
         }
       }
    }

    render(){
       return <RangeInput value={this.state.value} />;
    }
}


ReactDOM.render(
  <Application/>,
  document.getElementById('root')
);

Answer 1

I think this situation can be simplified quite a bit:

import React from 'react';

export const RangeInput = props => (
  <input
    value={props.value}
    onChange={props.setValue} />
)

export class Application extends React.Component {
  constructor(props) {
    super(props);
    this.state = { value: -1, };
  }

  componentDidMount() {
    var val = localStorage.getItem('myVal');
    if (val) this.setState({value: val})
  }

  setValue(e) {
    this.setState({value: e.target.value})
    localStorage.setItem('myVal', e.target.value);
  }

  render() {
    return <RangeInput
      value={this.state.value}
      setValue={this.setValue.bind(this)} />;
  }
}

Here we have two components: <RangeInput> , a stateless component, and <Application> , the brains behind the operation.

<Application> keeps track of the state, and passes a callback function to RangeInput. Then, on keydown, <RangeInput> passes the event object to that callback function. Application then uses the event object to update the state and the localStorage . On refresh, the last saved value is fetched from localStorage and present in the input (if available).