在 React 中访问嵌套的 JSON object

Question

数据集： https://disease.sh/v3/covid-19/historical/usa?lastdays=all

我是 React 的新手，正在尝试使用 COVID-19 跟踪器让我的脚湿透，所以请耐心等待...我正在尝试从上述数据集中访问时间轴 > 案例，但似乎无法使其工作。 我已经尝试let date in data.timeline.cases但这也不起作用。 也许我在寻找错误的地方 - 寻找一些指导。 谢谢！

const buildChartData = (data, casesType) => {
  let chartData = [];
  let lastDataPoint;

  for (let date in data.cases) {
    if (lastDataPoint) {
      let newDataPoint = {
        x: date,
        y: data[casesType][date] - lastDataPoint,
      }
      chartData.push(newDataPoint);
    }
    lastDataPoint = data[casesType][date];
  }
  return chartData;
};

function LineGraph({ casesType = 'cases' }) {
  const [data, setData] = useState({});

  useEffect(() => {
    const fetchData = async() => {
      await fetch('https://disease.sh/v3/covid-19/historical/usa?lastdays=120')
        .then((response) => {
          return response.json()
        })
        .then(data => {
          let chartData = buildChartData(data, casesType);
          setData(chartData);
        });
    };
    
    fetchData();
  }, [casesType]);

Answer 1

好的，正如您所说，您尝试let date in data.timeline.cases但您也需要更改代码的另一部分。

它不是data[casesType]而是data.timeline[casesType]

  for (let date in data.timeline.cases) {
    if (lastDataPoint) {
      let newDataPoint = {
        x: date,
        y: data.timeline[casesType][date] - lastDataPoint,
      }
      chartData.push(newDataPoint);
    }
    lastDataPoint = data.timeline[casesType][date];
  }