如何兑现空头承诺

Question

If the function GetTest returns value everything works fine, otherwise errors out. How can I properly handle empty promises? I tried this but I got:

Failed to load resource: the server responded with a status of 500 (Internal Server Error)

getTest = function (testId) 
{
    var promise = $http(
    {
        method: 'POST',
        url: self.baseUrl + 'Test/getTest',
        contentType: 'application/json',
        data: {
            testId: testId
        }
    });
    return promise;
}

 [HttpPost]
public ActionResult getTest(string testId)
{
    JsonResult jsonResult = new JsonResult();
    try
    {
        Test model = new Test();
        string returnValue = model.GetTest(Convert.ToInt32(testId));
        if(!string.IsNullOrEmpty(returnValue))
        {
            jsonResult.Data = returnValue;
            Response.StatusCode = 200;
            return jsonResult;
        }
        else
        {
            Response.StatusCode = 500;
            return Content("NoResult");
        }
     }
    catch (Exception ex)
    {
        return jsonResult;
    }
}

Answer 1

You can handle failed promises by using the second argument of .then() :

getTest()
    .then(
        function (result) {
            // handle result
        }, 
        function (error) {
            // request failed with error
        }
    );