javascript - 当数组已满时，Ajax 发送数组

Question

我有全局变量var distances = []。我有功能来填补它，但需要一些时间。我想在它填满时将其发送到 Django View 。然而，由于 JS 异步工作，我总是发送空数组。如何在不设置超时的情况下发送填充数组？我的js代码是

var distances = [] //array where some digits will be stored

function getAllDistances() //function where this digits being put in distances arr
//note that every digit is result of request to API of routing service so it takes 
//some time to get thing done

function ajaxTest(){//function for sending array to Django view
    $.ajax({
        url:'test/',
        type:'POST',
        data:JSON.stringify({distances : distances}),
        dataType: 'json',
        success:function (data) {
            console.log("Ajax test success");
            console.log(data.result.text);//view should return some result
        },

        error:function () {
            console.log("Ajax test failure")
        }
    })
}

function doTheJob(){ //main function 
    getAllDistances();
    ajaxTest();
}

所以请求一切正常，但它总是发送空数组。是否可以让js发送填充数组而不设置超时？我想回调会在这里做事，但如果我错了请纠正我

<小时/>

为了更清楚，我将添加获取距离的函数

function getRoutSummary(i, j, q) {
                    var url = 'https://router.project-osrm.org/route/v1/driving/' +
                            coords[i][1] + ',' + coords[i][0] + ';' +
                            coords[j][1] + ',' + coords[j][0] +
                            '?geometries=geojson';
//coord is array of arrays with coordinates like
//[[lat1, long1], [lat2, long2], [lat3, long3]] where lat is latitude and long 
//is longtitude

                    var req = new XMLHttpRequest();    
                    req.responseType = 'json';    
                    req.open('GET', url, true);    
                    req.onload = function () {
                        var jsonResponse = req.response;
                        var distance = jsonResponse.routes[0].distance;
                        distances[q] = distance;
                    };
                    req.send();
            }

然后我在循环中调用这个函数

function getAllDistances(){
                var q = 0;
                for (var i = 0; i < coords.length; i++){
                    for (var j = 0; j < coords.length; j++){
                        getRoutSummary(i, j, q);
                        q = q + 1;
                    }
                }
                console.log(distances);
            }

Answer 1

使用promises与 Promise.all()

distancePromise = [];

function getAllDistances() {
//a loop
var promise = getSingleDistance();
distancePromise.push(promise);
//return a array of promises
return distancePromise
}
//send the distances after all the promises have been resolved
Promise.all(distancePromise).then(function(distances) {
//save the distances
})