Category Archives: Web

Part 6: Custom Components – Tabs

In Part 4 we have seen how to use History.JS along with Crossroads.js to achieve proper client side routing and maintain browser state for proper back button navigation. However, SPAs often have complex page states for example a page with tabbed data or grid data with a particular filter.

One of the ways we can make a particular Tab of data ‘bookmark-able’ is by including the selected tab information as a part of the route. Thus, the particular tab becomes a part of the URL and can be navigated to directly or pushed to the browser history and retrieved on back button.

As you may have noted, our SPA has a name now – SilkThread and a site of it’s own Today we’ll create a Tab-Item component that will working with SilkThread’s routing mechanism.

Important: When I started this series KO Components was still in Beta, since then version 3.2.0 has gone live and is now available on Nuget also.This article onwards, I am using the release version from Nuget.

Before diving into custom components

We have been using ‘’magic strings” for representing routes, component names and so on. Multi-use components are used more than once, and complex views might be composed of multiple components. Relying on magic strings can be error prone and ‘difficult to maintain’. Why? Well imagine that you have created a component called drop-down in the drop-down folder. Now when you access it elsewhere you specify a magic string ‘drop-down’. But does the next person looking into your code know what it signifies? Is it the component name or the folder name or file name or just a random key? However if you accessed the string via a literal it will be amply clear that that string is for. So before our framework gets any more complex, let’s take a stab at cleaning up our magic strings.

The Component Registration

We add a new file called app.js in the /app folder. Mind you this is a first stab and we are likely to refactor later. Next we add the following code to it

app = {
components: {
greeter: {
name: ‘greeter’,
template: ‘App/components/greeter/greeting’
pages: {
home: {
name: ‘home’,
template: ‘App/pages/home/home’
settings: {
name: ‘settings’,
template: ‘App/pages/settings/settings’

As we can see this is a simple JS object that splits pages and components into different types and registers each sub object represents a component with two properties name and template to start off with.

Now we update our startup.js to use the appropriate component name and template names.

define([‘jquery’, ‘knockout’, ‘./router’, ‘app’, ‘bootstrap’, ‘knockout-projections’], function ($, ko, router) {
ko.components.register(, { require: app.components.greeter.template });

    ko.components.register(, { require: app.pages.home.template });
ko.components.register(, { require: app.pages.settings.template });
ko.applyBindings({ route: router.currentRoute });

Going forward, we’ll register our components via the app.components object.

Registering with Require

We have to tell Require there is a global app object now, so we update the require.config.js and add the app/app route the list.

var require = {
baseUrl: “/”,
paths: {

“app”: “app/app”


Getting a little JS help – Including Underscore.js

The Underscore.js library is a very handy toolset and has some nifty helper functions. I’ll explain the ones we use as I use them. To install it, just use the package-management console

PM> install-package underscore.js

The library is by default installed under the Scripts folder. I’ve moved it to the ‘Scripts\underscore’ subfolder.


Like the app.js earlier we’ll register Underscore in the require.config.js as well.

var require = {
baseUrl: “/”,
paths: {

“app”: “app/app”,
“underscore”: “Scripts/underscore/underscore”


With these two modifications to existing code set, we’ll start with the actual component.

Creating a Tab Component

A tab component has two parts, the tabbed header and the panel showing the tab’s content. If we consider the Tab as a menu item it could be a different page altogether. But at any given point a tab control shows only one panel, which is logically related to the selected tab.

To start off with we’ll create a component – tabbed-navigation. The tabbed-navigation component will be the top-level container that will be responsible for showing the tab headers and the selected tab’s container panel. The container panel will be a placeholder div that will be replaced by the component that needs to be shown for the selected tab. We can configure each tab to show a different component.

The tab-navigation HTML template

The HTML template in the app\components\tab-navigation\tab-navigation.html has the following markup:

<ul id=”tabHeader” class=”nav nav-tabs” role=”tablist”>
<!– ko foreach: tabs –>
<li data-bind=”css : {active : isSelected }”>
<a data-bind=”text : text, attr : { href: url }”></a>
<!– /ko –>

<div id=”tabPanel”
data-bind=”component: {name: selected().component, params: {name: selected().text }}”></div>

It has a simple layout using <ul> and the boot-strap styling classes nav and nav-tabs.

Inside the <ul> we loop through an array of tabs items which is going to be encapsulated in the tab-navigation.js view model.

In the loop we add a <li> that has the style active if the viewModel tab’s isSelected property is set to true. This sets the active style from Bootstrap.

In the <li> we have an anchor with two data-bindings. First is the text that’s going to be shown, next the url that’s bound to the href attribute.

Finally we have the <div> tabPanel. This is bound to a component which is initialized with the name and params properties. The name is bound to the selected tab’s component property (so our viewModel has to be able to return a selected tab). In params the only parameter we are currently sending is the name property, which is again picked up from the text property of the selected ViewModel.

The tab-navigation View Model and DataSource

From the above template we can probably guess of a data structure like the following

var ds = {
tabs: [
text: ‘selected 0’,
url: ‘/settings/tab0’,
isSelected : true
text: ‘selected 1’,
url: ‘/settings/tab1’,
isSelected: false
text: ‘selected 2’,
url: ‘/settings/tab2’,
isSelected: false
selected : function() {
// Return the tab that has isSelected = true;

To accommodate this structure we use two JS modules – tabsNavigationConfig.js and tabitemConfig.js


tabitemConfig = function (text, url, selected, component) {
self = this;
self.text = text;
self.url = url;
self.isSelected = selected;
self.component = component;
return self;


tabsNavigationConfig = function (tabitems, selectedIndex) {
self = this;
self.tabs = [];
for (var i = 0; i < tabitems.length ; i++) {
if (i == selectedIndex) {
self.tabs[i].isSelected = true;
return self;

The tabsNavigationConfig object has a constructor function that has the list of tabitemConfig objects and the index of which of the tabs is selected.

If you are still wondering as to why we are having a separate datasource for the component, it is simple. We want our component to be re-usable at multiple places, in the same page if required. Hence if we can decouple the data-source from the ViewModel we can configure any number of tab-navigation components with different data-sources. The ViewModel would only be concerned with the rendering and event handling limited to changing of the tabs.

The tab-navigation ViewModel

With the data source ready, we’ll setup the viewModel of the tab-navigation component. I have tagged each relevant line of code with an Index. You can click on them to see more details.

        “underscore”,                                          // #1
function (ko, _, tabbedNavigationTemplate) {                   // #2
var isInitialized = false;                                 // #3
var tabsCache = [];
var selectedIndexCache = 0;
function tabbedNavigationViewModel(params) {               // #4
self = this;
if (!isInitialized) {                                  // #5
isInitialized = true;
tabsCache = params.tabConfig().tabs;
self.tabs = ko.observableArray(tabsCache);             // #6
self.selectedIndex = ko.observable(selectedIndexCache);// #7
self.selected = ko.pureComputed(function () {          // #8
return self.tabs()[self.selectedIndex()];
}, this);
if (params.route) {                                    // #9
function selectByRoute(route) {                       // #10
var newTab = _.find(self.tabs(), function (tab) {   // #11
return tab.url == route();
if (newTab) {
self.tabs()[self.selectedIndex()].isSelected = false; //#12
var index = self.tabs().indexOf(newTab);      // #13
select(index);                                // #14
return item;                                      // #15
function select(index)                                // #16
selectedIndexCache = index;
self.tabs()[index].isSelected = true;
  return self;
return {
viewModel: tabbedNavigationViewModel,
template: tabbedNavigationTemplate };

#1: We start off by declaring that we refer to Underscore.js.
#2: Underscore is assigned to the variable _ Winking smile.

#3: We create three cache variables that are a part of the module rather than the viewModel constructor function. These are the list of tabs, the selected index and a flag indicating whether we have some cached information or not. When navigating to a tab we will get routed via the settings route. This will reinitialize the viewModel, so if we have the values cached we can use them instead of initializing the tabbed control everytime.

#4: The viewModel constructor function tabbedNavigationViewModel which takes in an initialization parameter, and may have a tabsConfig property. The tabsConfig has an array of tabs and the index of the selctedTab.

#5: We check if the module is being initialized the first time around. If so, we set the incoming tabs collection into the cache and mark the module as initialized.

#6: We initialize the tabs with the list in tabs cache.

#7: We set the default selectedIndex to 0.

#8: Pure Computed Observables: We have a new type of Observable introduced in KO 3.2.0 called the pureComputed. We know KO had computed observables that automatically updated themselves when their constituent observables changed. However, they suffered from one drawback. Computed observables were always triggered as soon as the constituent observables changed, even if the computed observable was not bound to a view element. This was a performance hit. To resolve this we now have pureComputed observables that get re-calculated only if they have subscriptions, i.e. someone is waiting to update itself based on changes in the pureComputed.

Here we have declared the selected property as a pureComputed and it returns the selected Tab. The selection changes whenever the selectedIndex changes. So anytime the selectedIndex changes the selected property returns the newly selected tab. As we will see in a bit, this renders a new container.

#9: We check if this viewModel is being created as a result of navigation (all cases except of first time page load). If it is due to navigation the route parameter is populated and we use it to select the particular sub-tab indicated by the route property.

#10: The selectByRoute function, called everytime the route changes.

#11: We use the Underscore library to find tab in the tabs collection. The syntax of _.find expects the array of items to look into and a comparison function to call for each element in the array. It returns the first element it finds.

#12: Once we’ve found the element we use the current selected index to set the isSelected flag to false for the current tab.

#13: We retrieve the index of the new selcted tab

#14: Next we call the select method.

#15: The select method sets the isSelected property of the new tab and updates the selectedIndexCache value for future use.

Initializing the Tab Component

Now that we’ve seen the structure of data we need and how that data is used lets see how we can use them. The Tab component is used inside the Settings Page component. So someone has to initialize it in the Settings page.

Tab Component markup in Settings.html

The markup to use the Tab Component is simple and unremarkable:

<tabbed-navigation params=”tabConfig : tabbedNavigation(), route: route()”>

There are two items being passed in the params property, tabConfig and route. The tabConfig property has the initialization parameters of how many tabs, their text, their URL and so forth. Refer to the tabNavigation viewModel section above.

The binding parameters imply that the Component View Model that’s backing this HTML has to provide he tabbedNavigation and route properties.

Tab Component viewModel code

Before now, the settings component was HTML only. We introduce the backing JS for this component. The code for it is as follows:

function (ko, settingsTemplate, _) {
var isInitialized = false;
var tabsNavigationInstance = null;
function settingsViewModel(params) {
var self = this;
self.tabbedNavigation = new ko.observable();
if (!isInitialized) {
isInitialized = true;
tabsNavigationInstance = init(params);
self.route = new ko.observable();
if ( {
return self;
function init(params) {
var newTabs = [];
for (var i = 0; i < 5; i++) {
var key = ‘tab’ + i;
newTabs.push(new tabitemConfig(
“Settings ” + i,
“/settings/” + key,
key ==,
tabsNavigationInstance = new tabsNavigationConfig(newTabs, 0);
return tabsNavigationInstance;
return { viewModel: settingsViewModel, template: settingsTemplate };

The crux of the component view model is the init method that’s called from the constructor function first time around. It need not be called init though. This function initializes an array and pushes in 5 instances of the tabitemConfig that we defined earlier. Since this is a demo we are simply doing a loop. For a real life scenario we would instantiate each instance with a relevant name and more importantly route to a component that should be visible when the tab is selected. In our case we are setting each route to point to the previously created ‘greeter’ component. So for every tab selection we’ll show a greeter component and if you refer back to the original markup at the top you’ll see we pass the selected tabs’ text property to the greeter as a parameter. So the greeter shows name of the tab selected.

Demo time

If we run the application and navigate to the Settings page we’ll see the following

– First tab ‘Settings 0’ is selected
– Greeter is saying Hello to ‘Settings 0’


– Clicking on Settings 1 tab, ‘navigates to that tab.Notice the route changes to settings/tab1. This corresponds to the route we setup when initializing the tabitemConfig object.


Now we can click on the Browser back button to navigate back to Settings 0 tab, and go forward again to come back to Settings 1 tab. When you navigate you’ll notice that the timestamp of Greeter component keeps changing this is because the greeter component doesn’t cache the time stamp so everytime the constructor function is called, the time gets updated.

Code for this version is available on the Part6 branch of the repository


In conclusion we saw how we could create a ‘tab-component’ using KO’s component model of development. Next we’ll see how we can use different components in different tabs and how to call server to get/put data.

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Building using NancyFX


Those who have been following my Knockout Component series of articles will know I am attempting to build a little SPA framework of my own here. No, it’s not the next best thing since sliced bread, just my attempts at learning Javascript, TypeScript and putting together a bunch of really cool libraries.

To try the entire thing online I decided to purchase a domain and the cheapest one was a .pw. SilkThread sounded like a nice name for a framework that was aiming to string together a series of well written libraries. So here we go, I am going to document my steps on creation of the first cut of, powered by Nancy and SilkThread itself Smile.

Who Nancy?

Well, it’s not a who, but a What. Nancy FX is an Open Source Web Framework in .Net. Conceptualized and initially built by Andreas Håkansson and supported by an awesome community of .NET devs, it’s now 3+ years old (here’s the list of the contributors). It is inspired by Sinatra in the Ruby world, but I don’t know enough about Sinatra to talk more about the history. It’s primary goal was to help build HTTP services in .NET. However, Nancy is more, it can serve up static content, html and even supports multiple view engines. So its like the best of both AspNET MVC and Web API worlds in one neat bundle.

Why NancyFX instead of AspNet MVC?

Well, no reasons really! Since my SPA effort is aimed at learning stuff and all of it is Open Source, I decided to try an Open Source framework that’s contemporary to the Asp.NET MVC!

My only requirement was that it should be host-able on IIS via my shared hosting provider. Once my Twitter pals Phillip Haydon and Filip Ekberg confirmed this is possible, I was all set to give it a go. I should also mention the gentle nudges from Phillip and Jonathan Channon to try out NancyFX contributed handsomely too Smile.

So no ‘political’ reasons, just an eager beaver trying out a new framework. You have already seen how to do everything I do here using ASP.NET MVC.

Getting Started

Nancy has some neat Visual Studio project templates, so you can get started directly using these templates. But that’s less of fun than learning things ground up. So I decided to start with an Empty Web template.


On clicking Ok, a new empty project is created, however we’ll see it has got a bunch of dependencies that I don’t think are required.


So we remove the ones shown selected above.

Next we add two Nancy packages from Nuget. If you are using Package Manager console you can get them using the following commands:

PM> install-package Nancy

PM> install-package Nancy.Hosting.AspNet

These two packages are all you need to get started.

A quick “Hello Nancy”

The Nancy equivalent of a ‘’AspNET MVC/WebAPI Controller” is the NancyModule. I have created a Modules folder and created added a HomeModule class in it. The Modules folder will hold our controller layer. In the root, I’ve added a IndexPage.html


Next I’ve updated the HomeModule to inherit from Nancy.Module.

In the constructor I’ve added a root path and assigned a method that returns a ViewRenderer. We’ve passed the IndexPage.html to the ViewRenderer because we don’t want any sever side processing done and want to show the HTML as is.

public class HomeModule : Nancy.NancyModule
public HomeModule()
Get[“/”] = GetIndex;

    private dynamic GetIndex(dynamic arg)
return View[@”/IndexPage.html”];

The IndexPage.Html simply says “Hello Nancy”.

<!DOCTYPE html>
<html xmlns=””>
Hello Nancy

With that set up, hit F5 and you should have a vanilla page on your default Browser as follows:


Well then, the myth of OSS projects being complex to get started with, stands BUSTED! Yes, Nancy is truly a low ceremony, awesome web framework.

But this is not what we want to setup do we? We want a nice Bootstrap Styled SPA! Well, let’s get to work.

Getting SilkThread into the project

To get SilkThread into the project, the best way would have been to get it via Nuget. But creating a Nuget package is a separate post, so we’ll use the age old technique of ‘copy-paste’. I have the latest code from the main branch of the project from Github. So I copied the App and Scripts folder into the project and re-arranged them a little. My new project structure is as follows:


I have made the following changes

  1. Created a Views folder and moved the Index.html to it.
  2. Created a Scripts/libs folder and moved all folders previous under Scripts to Scripts/libs
  3. Created a Scripts/app folder and moved the contents of the previous /App to Scripts/app
  4. The above folder realignment requires us to modify the Scripts/app/boot/require.config.js and change it as followsvar require = {
    baseUrl: “/
    paths: {
    “bootstrap”: “libs/bootstrap/bootstrap”,
    “historyjs”: “libs/history/native.history”,
    “crossroads”: “libs/crossroads/crossroads”,
    “jquery”: “libs/jquery/jquery-1.9.0″,
    “knockout”: “libs/knockout/knockout-3.2.0beta.debug”,
    “knockout-projections”: “libs/knockout/knockout-projections.min”,
    “signals”: “libs/crossroads/signals”,
    //”hasher”: “Scripts/crossroads/hasher”,
    “text”: “libs/require/text”
    shim: {
    “bootstrap”: {
    deps: [“jquery”]
  5. Next, install the bootstrap nuget package and removed the scripts folder as we already have the scripts in the libs folder.
  6. Finally we update the GetIndex method in the HomeModule to point to the Views/Index.htmlprivate dynamic GetIndex(dynamic arg)
    return View[@”

Now if we run the project we’ll get the following:


The ‘Oatmeal’ has greeted us! Nancy tries hard to tell us what happened and it seems it looked at lots of places but couldn’t find a file. Fear not, it’s a small detail but it’s a safe default.

Explicitly specifying content folders

Basically Nancy serves static content off the Content folder only by default (html files are served from any folder as long as you’ve got the routing right). So when our Index page is trying to access the Scripts folder, things are falling over. To use a custom folder structure like we defined above there are two options a. We move Scripts folder under Content and roll with it OR b. we tell Nancy about our folder structure. Let’s try the second option, it’s rather easy to do so.

  1. Add a new class called SilkThreadBootstrapper and inherit if from Nancy.DefaultNancyBootstrapper
  2. Override the method ConfigureConventions method and use the StaticContentConventionBuilder helper to add folders that you want Nancy to track.
  3. The full code is as follows, as you can see I’ve added the Scripts folder and the Views folderpublic class SilkThreadBootstrapper : Nancy.DefaultNancyBootstrapper
    protected override void ConfigureConventions(
    Nancy.Conventions.NancyConventions nancyConventions)


With those changes done, if we fire up our app, it will come up smoothly.



Deploying to the hosting Site

My host doesn’t support a fancy “Deploy from Github on commit to master’’ functionality. So I did it the amateur way:

  1. Got the IIS Web Publishing settings from my host
  2. Imported them into the project.
    Tear hair out because Web Publish keeps giving a weird error. Either provider or Visual Studio is broken.
  3. Enable ftp upload
  4. Setup ftp Deploy and Publish

Here you go!


(Note: I will be updating the site to be a little more useful so expect it to change over time).

If you look at the deployment folder it’s got only three dlls, with the total deployment size < 1MB. That’s pretty cool!



Nancy FX is a neat little framework with a tiny footprint for quick dash web projects. However, I have not even skimmed the surface of it’s abilities. To try out more I’ll continue to build SilkThread’s site using Nancy. So there will now be two streams of articles in parallel! One, features in SilkThread and the other about updates to the Site using Nancy.

Special Thanks to Phillip Haydon, for proofing the Nancy bits and pointing out some gotchas I comitted as a nOOb.

Source Code

The source code for is going to reside at Github, I’ll try to branch it as I go!

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