变量在函数更新值之前获取输出

Question

I have the following code that outputs the initialized value of my variable before it is updated by an $.ajax() callback. It seems that the 'get' is performed after the variable is logged despite how the code is written. How can I correct this? Thanks for any suggestions.

var statusUpdate = {
    queries : [],
    numQueries : 0,
    getNumQueries : function(){
        $.ajax({
            type: 'get',
            url: '40985839503175/planXML.txt',
            cache: false,
            error: function()
            { 

            },
            success: function(data){
                statusUpdate.queries = $(data).find('query');
                statusUpdate.numQueries = statusUpdate.queries.length;
                //console.log(statusUpdate.numQueries);

            }

        });

        }  // end getNumQueries

};


statusUpdate.getNumQueries();
console.log(statusUpdate.numQueries)

Answer 1

var statusUpdate = {
    queries : [],
    numQueries : 0,
    getNumQueries : function(){
        $.ajax({
            type: 'get',
            url: '40985839503175/planXML.txt',
            cache: false,
            error: function()
            { 

            },
            success: function(data){
                statusUpdate.queries = $(data).find('query');
                statusUpdate.numQueries = statusUpdate.queries.length;
                console.log(statusUpdate.numQueries);

            }

        });

        }  // end getNumQueries

};

Uncomment the logger in the success callback. Otherwise the log may run before the ajax call gets a chance to complete.

Answer 2

Ajax calls are asynchronous. I'm guessing that you are seeing 0 in your console?

Put the console.log inside the success function. But I'd recommend passing a callback or returning the promise object (it will require you to restructure your JavaScript).

var statusUpdate = {
    queries : [],
    numQueries : 0,
    getNumQueries : function(){
        $.ajax({
            type: 'get',
            url: '40985839503175/planXML.txt',
            cache: false,
            error: function()
            {

            },
            success: function(data){
                statusUpdate.queries = $(data).find('query');
                statusUpdate.numQueries = statusUpdate.queries.length;

                console.log(statusUpdate.numQueries)
            }

        });

        }  // end getNumQueries

};


statusUpdate.getNumQueries();

UPDATE : Here's what I meant by using a promise. For more info, see Deferred Object and the jQuery.ajax() documentation

var statusUpdate = {
    queries : [],
    numQueries : 0,
    getNumQueries : function(){
        var deferred = new $.Deferred();

        $.ajax({
            type: 'get',
            url: '40985839503175/planXML.txt',
            cache: false
        }).done(function(data){
                statusUpdate.queries = $(data).find('query');
                statusUpdate.numQueries = statusUpdate.queries.length;

                deferred.resolve();
        ).fail(function () {
            deferred.reject();
        });

        return deferred.promise();
    }  // end getNumQueries

};


statusUpdate.getNumQueries().done(function () {
    console.log(statusUpdate.numQueries)
});

Answer 3

Ok, I guess I can't make it work as envisioned. I added a complete function but it seems like kind of a workaround. Is this a reasonable practice? Thanks.