javascript - $.getJSON 带有 for 循环，仅在调试时起作用

Question

**我真的需要帮助，因为我无法找到可行的解决方案或自己完成。问题是，我无法获取信息。 “数据”应包括23个对象。问题是，在调试时一切正常。请帮我!!!我快要完蛋了。和回调或 then.(function...) 对我不起作用...;( **

function query_day2day(DateArray_){

        var Fluid_id = 0;
        var data_list = new Array();

    //read out the select element
        var e = document.getElementById("select_fluid");
        var Fluid_id = e.options[e.selectedIndex].value;
    //read in date
        //var d = document.getElementById("datepicker");
        //var date = d.value;
        var dateArray = new Array();
        dateArray = DateArray_;
    //Bring the date array in the correct form to submit
        for(i = 0; i<dateArray.length; i++)
        {
        var year = dateArray[i].substring(6, 10);   //substring(start, end)
        var month = dateArray[i].substring(0, 2); 
        var day = dateArray[i].substring(3, 5);  

        dateArray[i] = year + "-" + month + "-" + day;
        //alert(dateArray[i]);
        }

        for(i = 0; i<dateArray.length; i++)
        {
        switch (Fluid_id) {
            case '1':
               $.getJSON(setAddress_Event() + 'liter_hour/' + Fluid_id + '/' + dateArray[i], function(data){


                //data_callback(data, i); //I don´t understand this concept ;(
               data_list[i] = data;     


                });
                break;
            case '2':
               $.getJSON

已更新

        function getData(setAddress_Event, liter_hour, Fluid_id, dateArray){
          return $.getJSON(setAddress_Event + liter_hour + Fluid_id + "/" + dateArray).then(function(data){
            return {
              data_list:data
            }
          });
        }

        for(var j = 0; j<dateArray.length; j++)
        {
        getData(setAddress_Event(), "liter_hour/", Fluid_id, dateArray[j]).then(function(returndata){
          //received data!
          alert(j);
          data_collection[j] = returndata;

        });

        }


    alert(data_collection); //Hier ist data_list undefined und beim returnen wird es richtig übergeben.... ohne diesem alert wird falsch übergeben.... dreck
    return data_collection;

请帮助我，我需要所有数据而不仅仅是最后一个数据。调试正常，我不知道问题出在哪里......

Debugg Snippet

Answer 1

这是因为您在检索 JSON 的 Ajax 请求发回响应之前访问数据。请注意，当您执行时

    getData(setAddress_Event(), "liter_hour/", Fluid_id, dateArray[j]).then(function(returndata){
      //received data!
      alert(j);
      data_collection[j] = returndata;
    });

...内部函数未执行。它仅传递给 getData，并且您的代码会立即继续。只有当执行到脚本末尾时，Ajax请求才会一一调用你的回调函数，所以它们都会在主脚本结束后执行。

以下是处理该问题的方法(引入变量numPendingResults):

var numPendingResults = dateArray.length;
for(let j = 0; j<dateArray.length; j++) {
    getData(setAddress_Event(), "liter_hour/", Fluid_id, 
                                dateArray[j]).then(function(returndata){
      //received data!
      data_collection[j] = returndata;
      numPendingResults--; // one less to wait for!
      if (!numPendingResults) { // we have everything!
        console.log(data_collection);
        // anything you want to do with data_collection should be done here
        // ...
        // or call a function that will deal with it, from here.
      }
    });
}

您无法返回data_collection。相反，您应该调用如上所述的函数。该函数可能可以作为最外层函数的参数传递。或者进一步使用 Promise 系统。由您决定...