运行多个异步函数并等待结果

Question

我正在尝试为Google Maps API v3编写一个函数。基本上，我循环遍历给定形状的所有多边形点，并通过将每个点传递给将数据插入MySQL的PHP​​函数将它们添加到数据库中。

function saveSite() { 

     // Create an array to hold the individual point saving results 
     var submission_Result = []; 
     var final_result = true; 

     // Get the general properties for this shape 
     var shape_ID = selectedShape.ID; 
     var shape_Name = document.getElementById("info_name").value; 
     var shape_Description = document.getElementById("info_description").value; 
     var shape_Type = shapesArray[shape_ID].type;  

     var shape_Points = selectedShape.getPath(); 

     // Run through all points in the shape and save them 
     for (var i = 0; i < shape_Points.length; i++) { 
      var curPoint = shape_Points.getAt(i); 

      // Prepare the point data to be saved 
      var url = pageDir + "phpsqlinfo_addShapeData.php?db=" + database + "&job=" + jobnumber + 
         "&stype=" + shape_Type + "&snumber=" + shape_ID + "&sname=" + encodeURIComponent(shape_Name) + 
         "&sdesc=" + encodeURIComponent(shape_Description) + "&sseqno=" + i + "&slat=" + curPoint.lat() + "&slng=" + curPoint.lng(); 

      // Attempt to save the shape data 
      downloadUrl(url, function(data, responseCode) { 
       if (responseCode == 200 && data.length <= 1) { 
        submission_Result.push(true); 
       } else { 
        submission_Result.push(false); 
       } 
      }); 
     } 

     // Run through all point results and confirm correct submission of points 
     for (var i = 0; i < submission_Result.length; i++) { 
      if (submission_Result[i] == false) { 
       final_result = false; 
      }     
     } 

     // If all points were successfully saved, tell the user 
     if (final_result == true) { 
      // All points saved successfully so do something 
     } else { 
      // Something went wrong and not all points were added so do something else    
     } 
    } 

我知道* downloadURL *运行作为异步函数，因此我目前无法通过的* submission_result *阵列循环，并检查是否正确添加了所有点。 我的问题是，有没有什么办法可以等待所有的异步调用完成，然后检查结果数组？

也许这样的事情，例如?:

     }); 
     } 

     while (submission_Result.length < shape_Points.length) { 
      // Do something wait a short while 
     }; 

     // Run through all point results and confirm correct submission of points 
     for (var i = 0; i < submission_Result.length; i++) { 

任何想法，将不胜感激为我完全难倒！

在此先感谢。

Answer 1

你必须通过downloadUrl回调检查此，例如：

downloadUrl(url, function(data, responseCode) { 
    //... 

    if (submission_Result.length === shape_Points.length) 
     allResultsReady(); 
}); 

如果所有的结果都在，功能allResultsReady将被调用。

使用循环将阻止整个浏览器窗口，这绝对不是你想要的。