javascript - 如何通过错误处理执行 Ajax 请求并检测整体完成情况？

Question

再次出现某种伪同步问题......

我正在寻找在循环内完成所有 ajax 请求后运行函数的最佳实践。

坏例子:

var files = ["file1","file2","File3"];
var success = [];
var error = [];

for (var i = 0; i < files.length; i++) {
    $.ajax({
        type: "HEAD",
        url: files[i]
        }).done(function(){
            console.log("file found");
            success.push(files[i]);
            doThisWhenAllFilesChecked();
        }).fail(function () {
            console.log("file not found");
            error.push(files[i]);
            doThisWhenAllFilesChecked();
        })
}

错误示例 2:同步，只是为了说明我在寻找什么:

var files = ["file1","file2","File3"];
var success = [];
var error = [];

for (var i = 0; i < files.length; i++) {
    $.ajax({
        type: "HEAD",
        async: false, // <-- !
        url: files[i]
        }).done(function(){
            console.log("file found");
            success.push(files[i]);
        }).fail(function () {
            console.log("file not found");
            error.push(files[i]);
        })
}
doThisWhenAllFilesChecked();

Answer 1

你可以这样做-

 var files = ["file1","file2","File3"];
    var success = [];
    var error = [];
    var k = 0;
    for (var i = 0; i < files.length; i++) {
        $.ajax({
            type: "HEAD",
            url: files[i]
            }).done(function(){
                console.log("file found");
                 k++;
                success.push(files[i]);
                doThisWhenAllFilesChecked();
            }).fail(function () {
                 k++;
                console.log("file not found");
                error.push(files[i]);
               doThisWhenAllFilesChecked();
            })
    }

    function doThisWhenAllFilesChecked(){
      if(k==files.length){
        k = 0;
        //execute code here
      }
    }