Question

I am working on a web project that involves a cross-domain call, and I decided to use Knockout.js and ASP.NET Web Api. I used the Single Page Application template in VS 2012, and implemented the Knockout class as it is. The page works great when I make JSON call from the same domain, but when I try using JSONP from the remote server the knockout does not seem to bind the data. I can see the JSON data received from the remote while making JSONP call, but knockout cannot bind the data.

Here is my JavaScript ViewModel classes:

window.storyApp.storyListViewModel = (function (ko, datacontext) {
    //Data
    var self = this;
    self.storyLists = ko.observableArray();
    self.selectedStory = ko.observable();   
    self.error = ko.observable();

    //Operations
    //Load initial state from the server, convert it to Story instances, then populate self

    datacontext.getStoryLists(storyLists, error); // load update stories      

    self.selectStory = function (s) {
        selectedStory(s); $("#showStoryItem").click(); window.scrollTo(0, 0);
        storyItem = s;        
    }
    //append id to the hash for navigating to anchor tag
    self.backToStory = function () {        
        window.location.hash = storyItem.id;       
    }

    self.loadStories = function () {
        datacontext.getStoryLists(storyLists, error); // load update stories
    }

    return {
        storyLists: self.storyLists,
        error: self.error,        
        selectStory: self.selectStory
    };
})(ko, storyApp.datacontext);

// Initiate the Knockout bindings
ko.applyBindings(window.storyApp.storyListViewModel);

And my DataContext class as below:

window.storyApp = window.storyApp || {};

window.storyApp.datacontext = (function (ko) {

    var datacontext = {
        getStoryLists: getStoryLists
    };

    return datacontext;

    function getStoryLists(storyListsObservable, errorObservable) {
        return ajaxRequest("get", storyListUrl())
            .done(getSucceeded)
            .fail(getFailed);

        function getSucceeded(data) {
            var mappedStoryLists = $.map(data, function (list) { return new createStoryList(list); });
            storyListsObservable(mappedStoryLists);
        }

        function getFailed() {
            errorObservable("Error retrieving stories lists.");
        }

        function createStoryList(data) {
            return new datacontext.StoryList(data); // TodoList is injected by model.js
        }
    }

    // Private
    function clearErrorMessage(entity) {
        entity.ErrorMessage(null);
    }

    function ajaxRequest(type, url, data) { // Ajax helper
        var options = {
            dataType: "JSONP",
            contentType: "application/json",
            cache: false,
            type: type,
            data: ko.toJSON(data)
        };
        return $.ajax(url, options);
    }

    // routes
    function storyListUrl(id) {
        return "http://secure.regis.edu/insite_webapi/api/story/" + (id || "");
    }
})(ko);

This page: http://insite.regis.edu/insite/index.html makes the cross-domain call to secure.regis.edu, and it is not working. However the same page on secure.regis.eduinsite/index.html making JSON call works just fine.

What am I doing wrong? Any help will be greatly appreciated.

Answer 1

Thanks for those provided help.

I manage to solve the issue by adding WebApiContrib.Formatting.Jsonp class to my WebApi project as explained in https://github.com/WebApiContrib/WebApiContrib.Formatting.Jsonp, and making a slight modification to my jQuery Ajax helper class as below:

function ajaxRequest(type, url, data, callbackWrapper) { // Ajax helper
    var options = {
        dataType: "jsonp",
        crossDomain : true,
        type: type,
        jsonp: "callback",
        jsonpCallback: callbackWrapper,
        data: ko.toJSON(data)
    };   

    return $.ajax(url, options);
}

Everything worked as a charm.