使用 promise.all 从两个 api 获取数据

Question

I would like to get data from two API. in the firest call (getDatafromGeonames) I want to get latitude and longitude then I want to pass them as parameters to the second call (getWaetherData) to get weather information then I want to store the result and pass to my endpoint

Here is my try:

const res1 =   getDatafromGeonames(geonameAPIURL,city,geonamesKey).then(res =>{
          getWaetherData(res.address.lat, res.address.lng)})
  Promise.all([res1]).then((res)=>{
    //do somthing 
    console.log(res);
  })

a screenshot of the result:

I don't know why it is jumping to then and printing Undefined before it is executing getWaetherData? How can I get data from the first API then use these data to get weather info then do something with these data

thanks a lot:)

Answer 1

Promise.all only works for Promises you can run in parallel, you have to run them in sequence instead:

getDataFromGeonames(geonameAPIURL, city, geonamesKey)
  .then((res) => getWeatherData(res.address.lat, res.address.lng))
  .then((res) => {
    // do something
    console.log(res);
    return res;
  });

Answer 2

Promise.all(promises[]) method is meant to execute some logic when all promises[] has been executed. This would be helpful if you have 2 independant async calls and you want to do something after both of them has been executed.

By what you have described, seems that the second API call you have to do needs the result of the first API call, so the promise operator you should use is .then() .

const waetherData = getDatafromGeonames(geonameAPIURL,city,geonamesKey)
.then(res => getWaetherData(res.address.lat, res.address.lng))

or, in EMS6 style:

const getWaetherData = async (geonameAPIURL, city, geonamesKey) => {
      const geodata = await getDatafromGeonames(geonameAPIURL,city,geonamesKey);
      return await getWaetherData(geodata.address.lat, geodata.address.lng)
}

I have put this last code into a method because if you want to use await operator you need to be in a async context.