RequireJS, TypeScript and Knockout Components

Despite the teething problems I had getting my head around RequireJS, I had another go this week on sorting this out. The motivation for this was Knockout Components – re-usable asynchronous web components that work with Knockout. So this article details the steps required to make this work on a vanilla ASP.NET MVC website.


If you’re not familiar with components, they are similar to ASP.NET Web Controls – re-usable, modular components that are loosely coupled – but all using client-side JS and HTML.

Although you can use and implement components without an asynchronous module loader, it makes much more sense to do so and to modularise your code and templates. This means you can specify the JS code and or HTML template is only loaded at runtime, asynchronously, and on-demand.

Demo Project

To show how to apply this to a project, I’ve created a GitHub repository with a web app. Step one was to create the ASP.NET MVC application. I used .NET 4.5 and MVC version 5 for this but older versions would work just as well.

Next I upgraded all the default Nuget packages including JQuery so that we have the latest code, and then amended the home page to remove the standard ASP.NET project home page. So far, nothing new.


Next step is to add RequireJS support. At present our app loads the JavaScript modules synchronously from the HTML pages, using the ASP.NET bundler.

        public static void RegisterBundles(BundleCollection bundles)
            bundles.Add(new ScriptBundle("~/bundles/jquery").Include(

These are inserted via the _Layout.cshtml template:

    @RenderSection("scripts", required: false)

First we add RequireJS to the web app from the Nuget project, and the Text Addon for RequireJS. This is required to allow us to load non-JavaScript items (e.g. CSS and HTML) using RequireJS. We’ll need that to load HTML templates. These will load into the /Scripts folder.

Configuring RequireJS

Next, we create a configuration script file for RequireJS. Mine looks like this, yours may be different depending on how your scripts are structured:

    baseUrl: "/Scripts/",
    paths: {
        jquery: "jquery-2.1.1.min",
        bootstrap: "bootstrap.min"
    shim: {
        "bootstrap": ["jquery"]

This configuration uses the default Scripts folder, and maps the module ‘jquery’ to the version of JQuery we have updated to. We’ve also mapped ‘bootstrap’ to the minified version of the Bootstrap file, and added a shim that tells RequireJS that we need to load JQuery first if we use Bootstrap.

I created this file in /Scripts/require/config.ts  using TypeScript. At this point TypeScript is flagging an error saying that require is not defined. So now we need to add some TypeScript definition files. The best resource for these is the Github project Definitely Typed, and these are all on Nuget to make it even easier. We can do this from the Package Manager console:

   1: Install-Package jquery.TypeScript.DefinitelyTyped

   2: Install-Package bootstrap.TypeScript.DefinitelyTyped

   3: Install-Package requirejs.TypeScript.DefinitelyTyped

Implementing RequireJS

At this point we have added the scripts but not actually changed our application to use RequireJS. To do this, we open the _Layout.cshtml file, and change the script segment to read as follows:

    <script src="~/Scripts/require.js"></script>
    <script src="~/Scripts/require/config.js"></script>
    @* load JQuery and Bootstrap *@
        require(["jquery", "bootstrap"]);
    @RenderSection("scripts", required: false)

This segment loads require.js first, then runs the config.js file which configures RequireJS.

Important: Do not use the data-main attribute to load the configuration as I originally did –  you’ll find that you cannot guarantee that RequireJS is properly configured before the require([…]) method is called. If the page loads with errors, e.g. if the browser tries to load /Scripts/jquery.js or /Scripts/bootstrap.js then you’ve got it wrong.

Check the network load for 404 errors in the browser developer tools.

Adding Knockout

We add Knockout version 3.2 from the package manager along with the TypeScript definitions as follows:

install-package knockoutjs
Install-Package knockout.TypeScript.DefinitelyTyped

You need at least version 3.2 to get the Component support.

I then modified the configuration file to add a mapping for knockout:

require.config({ baseUrl: "/Scripts/", paths: { jquery: "jquery-2.1.1.min", bootstrap: "bootstrap.min", knockout: "knockout-3.2.0" }, shim: { "bootstrap": ["jquery"] } });

Our last change is to change the TypeScript compilation settings to create AMD output instead of the normal JavaScript they generate. We do this using the WebApp properties page:


This allows us to make us of require via the import and export keywords in our TypeScript code.

We are now ready to create some components!

Demo1 – Our First Component: ‘click-to-edit’

I am not going to explain how components work, as the Knockout website does an excellent job of this as do Steve Sanderson’s videos and Ryan Niemeyer’s blog.

Instead we will create a simple page with a view model with an editable first and last name. These are the steps we take:

  1. Add a new ActionMethod to the Home controller called Demo1
  2. Add a view with the same name
  3. Create a simple HTML form, and add a script section as follows:
    <p>This demonstrates a simple viewmodel bound with Knockout, and uses a Knockout component to handle editing of the values.</p>
    <form role="form">
        <label>First Name:</label>
        <input type="text" class="form-control" placeholder="" data-bind="value: FirstName" />
        @* echo the value to show databinding working *@
        <p class="help-block">
            Entered: {<span data-bind="text: FirstName"></span>}
        <button data-bind="click: Submit">Submit</button>
    @section scripts {
  4. We then add a folder views to the Scripts folder, and create a Demo1.ts TypeScript file.
// we need knockout
import ko = require("knockout");

export class Demo1ViewModel {
    FirstName = ko.observable<string>();

    Submit() {
        var name = this.FirstName();
        if (name)
            alert("Hello " + this.FirstName());
            alert("Please provide a name");

ko.applyBindings(new Demo1ViewModel());

This is a simple viewmodel but demonstrates using RequireJS via an import statement. If you use a network log in the browser development tools, you’ll notice that the demo1.js script is loaded asynchronously after the page has finished loading.

So far so good, but now to add a component. We’ll create a click-to-edit component where we show a text observable as a label that the user has to click to be able to edit.

Click to Edit

Our component will show the current value as a span control, but if the user clicks this, it changes to show an input box, with Save and Cancel buttons. If the user edits the value then clicks cancel, the changes are not saved.

image view mode and  image edit mode

To create this we’ll add three files in a components subfolder of Scripts:

  • click-to-edit.html – the template
  • click-to-edit.ts – the viewmodel
  • click-to-edit-register.ts – registers the component

The template and viewmodel should be simple enough if you’re familiar with knockout: we have a viewMode observable that is true if in view mode, and false if editing. Next we have value – an observable string that we will point back to the referenced value. We’ll also have a newValue observable that binds to the input box, so we only change value when the user clicks Save.

TypeScript note: I found that TypeScript helpfully removes ‘unused’ imports from the compiled code, so if you don’t use the resulting clickToEdit object in the code, it gets removed from the resulting JavaScript output. I added the line var tmp = clickToEdit; to force it to be included.

Registering and Using the Component

To use the component in our view, we need to register it, then we use it in the HTML.

Registering we can do via import clickToEdit = require(“click-to-edit-register”); at the top of our Demo1 view model script. The registration script is pretty short and looks like this:

import ko = require("knockout");

// register the component
ko.components.register("click-to-edit", {
    viewModel: { require: "components/click-to-edit" },
    template: { require: "text!components/click-to-edit.html" }

The .register() method has several different ways of being used. This version is the fully-modular version where the script and HTML templates are loaded via the module loader. Note that the viewmodel script has to return a function that is called by Knockout to create the viewmodel.

TypeScript note: the viewmodel code for the component defines a class, but to work with Knockout components the script has to return a function that is used to instantiate the viewmodel, in the same form as this script. To do this, I added a line  return ClickToEditViewModel; at the end of this module. This appears to return the class, which of course is actually a function that is the constructor. This function takes a params parameter that should have a value property that is the observable we want to edit.


Using the component is easy: we use the name that we used when it was registered (click-to-edit) as if it were a valid HTML tag.

<label>First Name:</label>
    <div class="form-group">
        <click-to-edit params="value: FirstName"></click-to-edit>

We use the params attribute to pass the observable value through to the component. When the component changes the value, you will see this reflected in the page’s model.

Sequence of Events

It’s interesting to follow through what happens in sequence:

  1. We navigate to the web URL /Home/Demo1, which maps to the controller action Demo1
  2. The view is returned, which only references one script “views/Demo1” using require()
  3. RequireJS loads the Demo1.js script after the page has finished loading
  4. This script references knockout and click-to-edit-register, which are both loaded before the rest of the script executes
  5. The viewmodel binds using applyBindings(). Knockout looks for registered components and finds the <click-to-edit> tags in our view, so it makes requests to RequireJS to load the viewModel script and the HTML template.
  6. When both have been loaded, the find binding is completed.

It’s interesting to watch the network graph of the load:


The purple vertical line represents when the page finished loading, after about 170ms – about half way through the page being completed and ready. In this case I had cleared the cache so everything was loaded fresh. The initial page load only has just over 33KB of data, whereas the total loaded was 306KB. This really helps make sites more responsive on a first load.

Another feature of Knockout components is that they are dynamically loaded only when they are used. If I had a component used for items in an observable array, and the array was empty, then the components’ template and viewModel would not be used. This is really great if you’re creating Single Page Applications.

Re-using the Component

One of the biggest benefits of components is reuse. We can now extend our viewModel in the page to add a LastName property, and use the click-to-edit component in the form again:

    <label>First Name:</label>
    <div class="form-group">
        <click-to-edit params="value: FirstName"></click-to-edit>
    <label>Last Name:</label>
    <div class="form-group">
        <click-to-edit params="value: LastName"></click-to-edit>

Now the page has two values using the same control, independently bound.

RequireJS – Shooting Yourself in the Foot Made Simple

I’ve run across a few JavaScript dependency issues when creating pages, where you have to ensure the right libraries are loaded in the right order before the page-specific stuff is loaded.

RequireJS seems like the solution to this problem as you can define requirements in each JavaScript file. It uses the AMD pattern and TypeScript supports AMD, so it looked like the obvious choice.

I’ve tried looking at RequireJS before briefly. A quick look was enough to make me realise this wasn’t a simple implementation, so until this weekend I had not made a serious attempt to learn it. Having tried to do this over a weekend, I’ve begun to realise why it’s not more widely used.


On the face of it, it seems that it should be simple. You load the require.js script and give it a config file in the data-main attribute, to set it up. When you write JavaScript code, you do so using AMD specifications so it can be loaded asynchronously and in the correct order.

For TypeScript users like myself, this presents a big barrier to entry (not RequireJS’s fault), as you need to specify the –module AMD flag on the compiler. This means all TypeScript code in the application is now compiled with AMD support, so existing non-requireJS pages won’t work. You have to migrate all in one go.

Setting Up a Test App

I created a simple ASP.NET web application with MVC to test requireJS, and followed the (many) tutorials, which explain how to configure the baseURL, paths etc. I then add a script tag to the _Layout.cshtml template to load and configure requireJS:

<script data-main="/Scripts/Config.js"


Seems simple enough, doesn’t it? In fact I’d just shot myself in the foot: I just didn’t realise it.

Since my original layout loaded jQuery and Bootstrap, I needed to replicate that, so I added the following code:

        require(['jquery', 'bootstrap'], function ($, bootstrap) {

This would tell requireJS to look for a javascript file called /Scripts/jquery.js, but since I loaded jQuery using Nuget the file is actually /Scripts/jquery-2.1.1.min.js

I obviously don’t want to bake that version number into every call or require() statement, so requireJS supports an ‘aliasing’ feature. In the config you can specify a path, in this format:

    paths: {
        "jquery": "jquery-2.1.1.min",
        "bootstrap": "bootstrap.min"

Requesting the ‘jquery’ module should now actually ensure that jquery-2.1.1.min.js is loaded.

Except that it doesn’t… most of the time.

Loading the page on both IE and Chrome with developer tools, I can see that mostly that require.js is trying to load /Scripts/jquery.js – what gives‽ Changing the settings and trying different combinations seems to have bearing on what actually happens.

I felt like a kid who’d picked up the wrong remote control for his toy car: it didn’t matter what buttons I pressed, the car seemed to ignore me.

StackOverflow to the Rescue (again)

I don’t like going to StackOverflow too quickly. Often, even just writing the question prompts enough ideas to try other solutions and you find the answer yourself.

In this case I’d spent part of my weekend and two days, hunting through lots of tutorials and existing StackOverflow answers, trying to figure out WTF was going on. Finally a kind soul pointed me to the right solution:

A config/main file specified in the in the data-main attribute of the require.js script tag is loaded asynchronously.

To be fair, requireJS does try to make this reasonably clear here – but this is just one little warning in the sea of information you are trying to learn.

This means that when you call require(…) you can’t be certain that the configuration is actually loaded or not. When I called require(..) just after the script tag for requireJS it had not been run, so it was using a default configuration.

What requireJS intended was that you load your modules just after setting the configuration, inside the config.js file. However, this approach only works if every page is running the same scripts.

So far the only way to get this to work has been to remove the data-main attribute and load Config.js as a separate script tag. At that point we can be sure the config has been applied and can specify dependencies and use aliases.

TypeScript files not compiling in VS2013 project

I created a C# class library project to hold some product-related code, and wanted to emit some JavaScript from this DLL, compiled from a TypeScript file. I added the .ts file and compiled the project, but no .js file was created.

The first thing to check is the Build Action is set to “TypeScriptCompile”, which it was – so why no .js output?

It seems the VS 2013 update 2 which is supposed to incorporate TypeScript compilation is not adding the required Import section to the project file.

If you add this line

  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)\TypeScript\Microsoft.TypeScript.targets" />

Just after the line

  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />

Then the TypeScript compiler will be invoked.

My thanks to my colleague Sri for figuring this one out!

Reported as a bug on Microsoft Connect:

TypeScript Debate

TypeScript was launched this month, and as Scott Hanselman notes it’s caused a lot of debate.

It seems a lot of people are prepared to wade in an denounce a system without trying to understand it. A good example is someone on Twitter with this opinion:

It’s about time we leave JavaScript alone and tell the ones who can’t seem to learn it to find another profession. #dart #typescript link

So his belief is that JavaScript is good enough and you don’t need any tooling.

I did reply to this tweet and was accused of personal attacks, when all I did was point out that his personal blog has JavaScript errors.

He misunderstood my meaning, complaining the errors were from code on the host site that was not his code. The point he missed was that JavaScript errors are everywhere. Writing good, reliable, tested JavaScript is very hard, even for professional companies like and Yahoo.

I did a bit of research and found a survey of JavaScript errors in top 100 sites.

I realised @TheMarco must be a JavaScript guru who has gone through the pain of learning all the odd little quirks and techniques of JavaScript. And now he sees neophyte developers just bypassing all this with tools like CoffeeScript, Dart and TypeScript doing all the hard work for them. “It’s not fair!” he rages. A bit like my children.

He is a portrait painter of the nineteenth century, who is suddenly faced with the invention of photography.

Surely anything that makes it easier to write solid, testable code has to be a good thing?