TypeError：无法读取未定义的属性“未定义”

Question

我有这个数组：

        super(props);
        this.state = {
            data: [{
                baseCurrency: 'GBP',
                baseAmount: 0,
                convertToCurrency: 'USD',
                rates: [],
                currencies: []
            },
                ]
        }

当我尝试在 render() function 中访问它时，它给了我错误

const {货币，汇率，baseCurrency，baseAmount，convertToCurrency} = this.state.data;

常量结果 = Number.parseFloat(baseAmount * rates[convertToCurrency]).toFixed(2);

如果我没有用数组声明 this.state，那么这个问题就不会发生。

Answer 1

您只能传播特定的 object 因为this.state.data是一个数组：

const [
  { currencies, rates, baseCurrency, baseAmount, convertToCurrency },
] = this.state.data;

并且更具可读性：

const [firstItem] = this.sate.data;
const {
  currencies,
  rates,
  baseCurrency,
  baseAmount,
  convertToCurrency,
} = firstItem;

Answer 2

像这样解构数据

 let res = { data: [{ baseCurrency: 'GBP', baseAmount: 0, convertToCurrency: 'USD', rates: [], currencies: [] }, ] } const { data: [{ baseCurrency, baseAmount, convertToCurrency }] } = res; console.log(baseCurrency, baseAmount, convertToCurrency);