错误数组Ajax承诺使用“何时”

Question

I'm having an error when using several ajax calls, I put this in an array and I need capture when finish all. My code is this:

var userId=[1,2,3];
var ajaxR = [];
for (var us in userId) {
    var usId = userId[us];
    ajaxR.push($.ajax({
        type: "GET",
        async: true,
        contentType: "application/json; charset=utf-8",
        dataType: "json",
        url: "myurl",
        data: { id: usId }   
    }));
}
$.when.apply($, ajaxR).always(function (e) {
    //Here I have the error but arguments it's ok
    var objects = arguments;      
});

When I debbug this code I have an error in $.when function:

Uncaught TypeError: Cannot read property '0' of undefined

Update:

My complete function is it:

 function UserFromWS(userId) {
        var users = [];
        var ajaxR = [];
        for (var us in userId) {
            var usId = userId[us];
            ajaxR.push($.ajax({
                type: "GET",
                async: true,
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                url:  "url",
                data: { id: usId }   
            }));
        }
        $.when.apply($, ajaxR).always(function (e) {
            var obj = arguments;
            return obj;
        }); 
        // return users;
    }

The error disapear if I put return users; in end of function. But it finish returning users array empty, before return obj. I need call the function in this way:

var allUsers = UserFromWS ([1,2,3]);

The function should return obj in $.when promise.

Answer 1

Fist thing to check is that "userId" is being passed as an array. Then the for loop need to be modified to correctly loop the array ( Why is using "for...in" with array iteration a bad idea? ).

Also the function needs to return a promise:

 function UserFromWS(userId) {
        var users = [];
        var ajaxR = [];
        for (var i = 0; i< userId.length; i++) {
            var usId = userId[i];
            ajaxR.push($.ajax({
                type: "GET",
                async: true,
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                url:  "url",
                data: { id: usId }   
            }));
        }
        return $.when.apply($, ajaxR).done(function (e) {
            var obj = arguments;
            return obj;
        }); 
        // return users;
    }

Also you will need to wait for the result of this function:

var users = [10];

UserFromWS(users).then(function(result) { /* do stuff now */ });

Answer 2

Why do you save the ajax call to array, JQuery can recongnize the request by himself, and you can call the same $.ajax() many times without error.

Example:

       $.ajax({
            type: "GET",
            async: true,
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            url:  "url",
            data: { id: usId }   
        }).done(function (e) {
        var obj = arguments;
        return obj;
    });

Or if you want to continue with your system, know that when use promise see https://api.jquery.com/jquery.when/