Node.js承诺链不会同步运行

Question

Maybe I'm misunderstanding promises (again) but my promise chain isn't waiting for the previous promise to resolve before moving onto the next.

Here is my code:

function getLocations(){
  return new Promise((resolve, reject) => {
    request('https://api.sportradar.us/ncaamb/trial/v4/en/polls/ap/2017/rankings.json?api_key=MY_KEY', function (error, response, body) {
      resolve(body);
    });
  })
}

function convertLocations(body){
  return new Promise((resolve, reject) => {
    for(var i=0; i<15; i++){
      myLocation = JSON.parse(body).rankings[i].market

      var geocodeParams = {
        "address": myLocation
      }

      gmAPI.geocode(geocodeParams, function(err, result){
        areaLat = result.results[0].geometry.location.lat.toFixed(2);
        areaLong = result.results[0].geometry.location.lng.toFixed(2);
        console.log(areaLat + "  " + areaLong);
        locationString += areaLat + "  " + areaLong + "|";
      });

      params["markers"].push({location: myLocation})
    }

    resolve(locationString);
  })
}


getLocations()
.then((body) => convertLocations(body))
.then((locationString) => {
  console.log("HERE ---> " + locationString);
})

So the last thing that i want to be output in the console.log("HERE ---> " + locationString); but it gets output before anything else instead.. why is the last function in the promise chain not waiting for the other promises to resolve?

Answer 1

Try this:

function getLocations() {
  return new Promise((resolve, reject) => {
    request('https://api.sportradar.us/ncaamb/trial/v4/en/polls/ap/2017/rankings.json?api_key=MY_KEY', function (error, response, body) {
      resolve(body);
    });
  })
}

function convertLocation(location) {
  return new Promise((resolve, reject) => {
    // do whatever you need to convert, i'm not sure if i was careful enough when I copy-paste you code

    var geocodeParams = {
      "address": myLocation
    }
    gmAPI.geocode(geocodeParams, function (err, result) {
      areaLat = result.results[0].geometry.location.lat.toFixed(2);
      areaLong = result.results[0].geometry.location.lng.toFixed(2);
      console.log(areaLat + "  " + areaLong);
      resolve(areaLat + "  " + areaLong + "|"); // <---- reosolve promise !!!
    });

  })
}

function convertLocations(body) {

  var promises = [];
  var data = JSON.parse(body);


  for (var i = 0; i < 15; i++) {
    promises.push(convertLocation(data.rankings[i].market));
  }

  return Promise.all(promises).then(arrayOfResulst => {
    return arrayOfResulst.join('')
  })
}


getLocations()
  .then((body) => convertLocations(body))
  .then((locationString) => {
    console.log("HERE ---> " + locationString);
  })

I'm not pretty sure I copied all correctly, and code could be written better (eg use reduce instead of for-loop), but i hope it will show you main idea.