如何使用for循环将数据从fetch（）推送到Javascript中的数组？

Question

我正在尝试从存储在数组中的几个URL中获取数据。每个网址都包含json格式的数据。我正在使用for循环遍历存储在url数组中的url。每个json文件都包含我感兴趣的travelTimeInSeconds值。运行以下代码时，存储在timeT变量中的两个值将记录在控制台中。但是，ttTimes数组保持为空。如何获取要存储在ttTimes数组中的值？

urls = ['www.a.com/dataa.json','www.b.com/datab.json']
ttTimes = []

function getData(url) {
    fetch(url)
    .then(response=>{
        return response.json()
    })
    .then(data =>{
        let timeT = Math.round(data['routes'][0]['summary']['travelTimeInSeconds']/60); 
        console.log(timeT)
        ttTimes.push(timeT)
    })

}

for (url in urls){
    time = getData(urls[url])
    console.log(time)
    ttTimes.push(time)
};

Answer 1

ttTimes数组保持为空，因为您从不等待对promise的解析，然后再对其进行检查。您可以使用Promise.all等待所有命令，然后再检查结果数组。

urls = ['www.a.com/dataa.json','www.b.com/datab.json']

// This function just returns a promise
function getData(url) {
  return fetch(url)
    .then(response=>{
      return response.json()
    })
    .then(data =>{
      const timeT = Math.round(data['routes'][0]['summary']['travelTimeInSeconds']/60); 
      return Promise.resolve(timeT);
    })
}


Promise.all(
  // use the urls to create an array of promises
  urls.map(getData)
).then((ttTimes) => {
  // When all the promises have been resolved, then this will be executed
  //Here all the promises have been resolved, so you would have an array with the ttTimes
  console.log(ttTimes);
})