如何知道javascript所有异步操作何时结束？

Question

我在我的网站上启用了WCF-Ajax。

我需要异步保存文件，但最终我需要知道所有异步操作何时完成。

function test() 
{ 
    for (var i = 0; i < arr.length; i++) { 
     saveFileService.SaveFile(arr[i], onSaveFileComplete); 
    } 

    //TODO: CHECK THAT **ALL** FILE SAVES ARE DONE 
} 

function onSaveFileComplete(result) 
{ 
    // ONE FILE SAVE ENDED SUCCESSFULLY 
} 

如何编写“TODO”部分？

Answer 1

只需使用一个全球性的反...

var fiesCurrentlySaving = 0; 

function test() 
{ 
    for (var i = 0; i < arr.length; i++) { 
     // Increase counter for the number of files saving 
     filesCurrentlySaving++; 

     // Save the file 
     saveFileService.SaveFile(arr[i], onSaveFileComplete); 
    } 
} 

function onSaveFileComplete(result) 
{ 
    // Reduce the file counter 
    filesCurrentlySaving--; 

    if (filesCurrentlySaving <= 0) 
    { 
     // Do whatever you need to do now! 
    } 
} 

Answer 2

您可以维护一个计数器变量并在完成回调中增加它。当它到达arr.length时，所有文件都将被处理。

是这样的：当你保存文件

function test() 
{ 
    var processedFiles = 0, fileCount = arr.length; 
    for (var i = 0; i < fileCount; i++) { 
     saveFileService.SaveFile(arr[i], function() { 
      // One file save ended successfully. 
      if (++processedFiles == fileCount) { 
       // All files have been processed. 
      } 
     }); 
    } 
} 

Answer 3

试试这个

function test() 
{ 
    for (var i = 0; i < arr.length; i++) { 
saveFileService.SaveFile(arr[i], onSaveFileComplete); 
    if(i == arr.length) 
    { 
     //TODO: CHECK THAT **ALL** FILE SAVES ARE DONE 
    } 
} 
}