Javascript 在函数中，返回值不分配给变量

我尝试使用带getMidPoint函数的多边形查找三个不同位置的三个中点。同时尝试在getMidPoint函数中返回数组。数组值没有分配给midPoints变量，我在terminal中将无法读取未定义的属性“length”作为错误

var midPoints = getMidPoint(Location1, Location2)
    // Directions API
    var i = 0;
    var array = [];
    function getMidPoint(a, b) {
        console.log("I am working...")
        clientMap.post(config_KEYS.DIRECTION_API + a + "&destination=" + b + "&key=" + config_KEYS.GOOGLE_API_KEY + "&departure_time=" + timeStamp + "", function (googleDirectionData, error) {
            if (googleDirectionData.status == "ZERO_RESULTS" | googleDirectionData.status == "INVALID_REQUEST") {
                res.status(400).send(googleDirectionData)
            }
            else {
                var polyline = googleDirectionData.routes[0].overview_polyline.points
                var decoded = decode(polyline)                
                var n = Math.round(decoded.length / 2)
                var obj = {}
                obj.latitude = decoded[n].latitude
                obj.longitude = decoded[n].longitude
                array.push(obj)   
            }  
        })
        return array    
    }

    if (midPoints && midPoints.length == 1) {
        console.log("durationpointDat   dfggdfg"+ midPoints.length)
        var durationpointData2 = getMidPoint(Location2, Location3)
    }
    else {
        if (midPoints.length == 2) {
            console.log("durationpointData fdf"+ midPoints.length)
            var durationpointData3 = getMidPoint(Location3, Location1)                        
        }
        else{
                res.status(200).json(array)
        }
    }

---

建议将不胜感激。

尝试在函数中声明var数组并返回它。不在全局范围内

正如我在getMidPoint中看到的那样，您正在调用google map API。异步调用意味着在完成GoogleAPI调用之前，您的代码正在执行下一个代码，因此在中点，您将无法定义

表示在完成google map api之前返回数组。您必须创建一个回调并将数据传递给它

你可以遵循这个例子

var midPoints;
getMidPoint(Location1, Location2, function(error,data){
    // You can check for error here
    midPoints = data;
})
// Directions API
var i = 0;
var array = [];
function getMidPoint(a, b, callback) {
    console.log("I am working...")
    clientMap.post(config_KEYS.DIRECTION_API + a + "&destination=" + b + "&key=" + config_KEYS.GOOGLE_API_KEY + "&departure_time=" + timeStamp + "", 
        function (googleDirectionData, error) {
        if (googleDirectionData.status == "ZERO_RESULTS" | googleDirectionData.status == "INVALID_REQUEST") {
            res.status(400).send(googleDirectionData)
        } else {
            var polyline = googleDirectionData.routes[0].overview_polyline.points
            var decoded = decode(polyline)                
            var n = Math.round(decoded.length / 2)
            var obj = {}
            obj.latitude = decoded[n].latitude
            obj.longitude = decoded[n].longitude
            array.push(obj)
            callback(null, array);
        }  
    }) 
}

---

是的，我在函数中分配了数组，但返回数组语句值未分配给中点，且中点长度未定义