Using npm packages with Blazor

Kedren Villena
Aug 9, 2019 · 5 min read

Blazor is an amazing Web UI Framework since you can now use C# on front end web applications. However, there are times when you still need to use modern JS libraries especially ones provided via npm

So how do you use JS modules provided via npm ?


  • .NET Core 3.0 is installed
  • NodeJS is installed

Let’s build a Blazor application from scratch:

$ dotnet new blazorserverside --auth Individual

This will create a new Blazor application.

Let’s try to run this:

$ dotnet run

It’s working as expected.

For the npm module that we are going to use, we’ll use moment which is a simple module for handling time in JS.

Let’s create a folder named JsLib in our Blazor application:

We’ll now initialize a new npm project inside the JsLib folder:

$ cd JsLib

$ npm init

Just leave an empty response to the questions. We’re not gonna focus on them.

Create a new directory src inside the JsLib folder and create a new file named index.js :

The index.js will serve as the “root” for exposing the libraries that we are gonna be using.

We’ll now add moment via npm. Execute this in the JsLib directory:

$ npm install moment

The package.json should now contain the following:

Next, we’ll create a new file called time_lib.js in the src folder:

Add the following code:

We’ll now call it in the index.js and expose a function that the Blazor app can call:

In the above example, the JsInterop for Blazor will be calling the GetCurrentTime() function.

We’ll now use webpack to bundle our library and put the output inside the wwwroot/js in out Blazor application.

Go to the JsLib folder and run this command:

$ npm install webpack webpack-cli

This will add the dependencies to webpack and webpack-cli which we’ll be using to bundle our library. The dependencies folder should now include webpack and webpack-cli :

Now we’ll create the webpack.config.js inside the JsLib folder which will handle the configurations for webpack :

Add the following contents inside the webpack.config.js :

The configuration above will tell webpack to do the following:

  • Use babel-loader since we are using ES6 syntax.
  • Name the bundled library my_lib.js and set the root library that will be attached to window (for client-side) and name it as MyLib . More on to this later on.
  • Place the bundled library to wwwroot/js .

Now we’ll update the package.json to add a build that will call webpack .

Add this to the “scripts” section in the package.json :

"build": "webpack --mode production"

The package.json will now look like this:

Since we used ES6 syntax, we need to add babel dependencies. Run this command on the JsLib folder:

$ npm install babel-loader @babel/core --save-dev

This will add the needed babel dependencies for webpack to properly bundle our library. The resulting package.json will now be:

Let’s now build our library using this command:

$ npm run build

This will build the library and output our bundle to the wwwroot/js folder:

As you can see, our my_lib.js is now in the wwwroot/js folder of our Blazor application.

Let’s now use our library on our Blazor application :)

We’ll start with adding our library to the JS files used by our Blazor application. In _Host.cshtml , add the following line:

<script src="js/my_lib.js"></script>

The body of _Host.cshtml should look something like this:

Let’s run our Blazor application first and see that our library is actually there. After running, open the browser (mine is Chrome) and see that the window actually has our library:

The reason why window actually got MyLib is because of library property in the output of webpack.config.js .

Since this is now part of the window , we can now call it in our Blazor application :)

Create a new page in the Pages directory and name it as Time.razor :

Time.razor will contain the following code:

The code above uses Blazor’s JsInterop and invokes the MyLib.GetCurrentTime from our library.

Run your Blazor application and navigate to /time :

Press the button and you’ll get the result from the library that we have created :)

As you can see, we can now use npm modules and expose them as libraries to our Blazor application :)


Integrating our npm run build to our dotnet build :)

Modify your .csproj file to something similar to the one below:

The idea from that one was copied from the react-redux template. The short summary is that npm calls are integrated to dotnet’s build command.

On publish, the library is copied over to the wwwroot/js folder so no need to configure anything for releases.

Here’s a sample dist folder after running dotnet publish -o dist :

As you can see, the my_lib.js is first copied to the source directory so that when dotnet builds it, it’s already there.

Note that there are still tons of optimizations that can be done here. But at least we can see that npm modules can be used as libraries for Blazor applications :)

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Kedren Villena

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Kedren Villena

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