javascript - 为什么当我开始使用 localStorage 时代码停止工作？

Question

下面的代码仅在我删除使用 localStorage 的 componentWillMount 时才有效。使用 localStorage 会出现错误

this.state.interests.map is not a function

我尝试将 localStorage 的使用移出组件，但没有帮助。我认为使用本地存储会以某种方式改变 this.state.interests，它们不再是一个数组。

let interests = ["Музыка", "Компьютеры", "Радио"]
let ListOfInterest = React.createClass({
  getInitialState: function() {
    return {value: '', interests: interests};
  },
  componentWillMount() {
    let local = localStorage.getItem('interests')
    if (local) {
      this.setState({interests: local});
    } else {
      localStorage.setItem('interests', this.state.interests)}
  },
  deleteInterest(key) {
    delete interests[key]
    this.setState(this.state) // without this line the page will not re-render
  },
  addInterest() {
    interests.unshift(this.state.value)
    this.setState({value: ''})
  },
  handleChange(event) {
    this.setState({value: event.target.value})
  },
  render() {
    return <div className="interests">
      <b>Интересы</b>
      <br/>
      {this.state.interests.map((int, index) => {
        return <button onClick={() => {
          this.deleteInterest(index)
        }} key={index} className="btn-interest">{int}</button>
      })}
      <input type='text' placeholder="Add" value={this.state.value} onChange={(e) => this.handleChange(e)}/>
      <button onClick={() => {
        this.addInterest()
      }} className="add">Add interest</button>

    </div>
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

Answer 1

您的示例中有几个问题

1. 在localStorage.setItem中第二个参数必须是String，你不能存储Array(当你这样做，在存储中将以逗号分隔字符串，因为调用方法 toString - [1, 2, 3].toString() )，您需要 stringify设置为存储之前的数组

   keyValue A DOMString containing the value you want to give the key you are creating/updating.

   localStorage.setItem(
      'interests', JSON.stringify(this.state.interests)
   )
   

   获取值时为parse

   let local = JSON.parse(localStorage.getItem('interests'));
   

2. this.setState(this.state) 这不是更新状态的好方法，您需要像这样更新状态

   deleteInterest(key) {
     this.setState({
       interests: this.state.interests.filter((el, i) => i !== key)
     })
   },
   
   addInterest() {
     this.setState({ 
       value: '', 
       interests: this.state.interests.concat(this.state.value)
     });
   },
   

Example