javascript - 控制台日志不记录

Question

我有这段代码

import axios from 'axios';
import {
  CURRENCY_RATE, 
  CURRENCY_FETCHING, 
  CURRENCY_ERROR
 } from './type.js';

import {
  CurrencyRateLink
} from '../urls.js';
import {currencyDetails} from './currencyDetails'


export const CurrencyRate = (selectedCurrency) => {
  return function (dispatch) {
    dispatch({type: CURRENCY_FETCHING})
    axios.get(CurrencyRateLink).then((response) => {
      let Currency = []
      if ( selectedCurrency != "USD") {
      let CurrencyRates = Object.keys(response.data.rates)
        for (let i=0; i<CurrencyRates.length; i++) {
           if (selectedCurrency == CurrencyRates[i]) {

             console.log("inside If condition")
            let currencySymbol = currencyDetails[selectedCurrency][symbol]
             console.log(currencySymbol)

              Currency.push({
              currencyName : CurrencyRates[i],
              currencyPrice : response.data.rates[selectedCurrency]
              })
           }
        }

      }
    return (
    dispatch({
      //Dispatching Redux Action
    })
  )}).catch((error) => dispatch({
      //Error Handling
   }))
  }

这里这条语句没有记录任何内容

console.log(currencySymbol)

但是它上面的语句正在登录控制台日志

console.log("inside If condition")

[问题:]可能做错了什么？

[注意:] 当我执行类似 let currencySymbol = currencyDetails[selectedCurrency] 的操作时，currencyDetails[selectedCurrency] 可能不存在，但随后它不应该记录 undefined 或抛出错误而不是不记录任何东西吗？

[更新:]我正在研究 React-native

Answer 1

您可能会收到 Uncaught TypeError: Cannot read property XXX of undefined 但在您的 React Native CLI 上不可见。如果currencyDetails[selectedCurrency] == undefined，就会出现上面的错误情况

试试下面的代码:

let currencySymbol = (currencyDetails[selectedCurrency]) ? currencyDetails[selectedCurrency][symbol] : null
console.log('result', currencySymbol)

至少你应该得到 result null