为什么当我开始使用localStorage时代码停止工作? [英] Why the code stops working when I start using localStorage?

问题描述

下面的代码仅在删除使用localStorage的componentWillMount时有效.用法localStorage会导致错误

The code below is only working when I remove the componentWillMount that uses localStorage. With usage localStorage it gives a mistake

this.state.interests.map不是函数

this.state.interests.map is not a function

我试图将localStorage的使用移出组件，但这无济于事.我想使用本地存储会以某种方式更改this.state.interests，使其不再是数组.

I tried to move usage of localStorage out of component but it won't help. I suppose that using local storage somehow changes this.state.interests that they stop being an array.

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>

推荐答案

示例中有几个问题

localStorage.setItem第二个参数中的

1. 必须是String，您不能存储Array(时，由于调用方法toString，所以在存储中将用逗号分隔字符串. -[1, 2, 3].toString() )，则需要

1. in localStorage.setItem second argument have to be a String, you can not store Array(when you do it, in storage will be string separated by coma because called method toString - [1, 2, 3].toString() ), you need stringify array before set to Storage

keyValue 包含以下内容的DOMString:您想要赋予的价值 您正在创建/更新的密钥.

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

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

和 parse 获得价值时

and parse when get value

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

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

this.setState(this.state) this is not good way to update state, you need update state like so

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

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