Javascript异步/等待for循环

Question

I have a problem

async function checkOk(listNotOkLocation) {
    // console.log(listNotOkLocation)
    var lenNotOk = listNotOkLocation.length
    if (lenNotOk == 0) return 'green'
    var latMarker = markerLocation.getPosition().lat()
    var lngMarker = markerLocation.getPosition().lng()
    var origin = latMarker.toString() + ", " + lngMarker.toString()

    for (var i = 0; i < lenNotOk; i++) {
        var lat = listNotOkLocation[i].lat
        var lng = listNotOkLocation[i].lng
        var destination = lat.toString() + ", " + lng.toString()
        calcRoute(origin,destination, function (err, dist) {
            console.log(1)
            if (!err) {        
                if (dist <= minDistance) 
                    return 'red'
            }
        });
    }
    console.log(2)
    return 'green'
}

Function calcRoute in for loop takes time, so function checkOk always returns 'green'. Can someone help me to solve this problem?

Answer 1

wrap your calcRoute into something that returns a promise

function calcRouteP(origin, destination) {
  return new Promise((resolve, reject) => {
    calcRoute(origin, destination, function (err, dist) {
      if (err) {
        reject(err);
      } else {
        resolve(dist);
      }
    });
  });
}

Then use it in your async function

async function checkOk(listNotOkLocation) {
    // console.log(listNotOkLocation)
    var lenNotOk = listNotOkLocation.length
    if (lenNotOk == 0) return 'green'
    var latMarker = markerLocation.getPosition().lat()
    var lngMarker = markerLocation.getPosition().lng()
    var origin = latMarker.toString() + ", " + lngMarker.toString()

    for (var i = 0; i < lenNotOk; i++) {
        var lat = listNotOkLocation[i].lat
        var lng = listNotOkLocation[i].lng
        var destination = lat.toString() + ", " + lng.toString()
        var dist = await calcRouteP(origin,destination);
        if (dist <= minDistance) {
          return 'red'
        }
    }
    console.log(2)
    return 'green'
}

note that for functions who's last argument is a callback that is passed err, result like your calcRoute function there are often libraries to do the wrapping for you. In node.js instead of wrapping calcRoute yourself you can do this

const util = require('util');
const calcRouteP = util.promisifiy(calcRoute);