Dynamically Add JavaScript in Blazor Components
How To Blazor .NET Core

Dynamically Add JavaScript in Blazor Components

Editorial Team
Mishel Shaji
Editorial Team, Mishel Shaji

Blazer is a new single-page web application development from Microsoft. Blazor allows .Net developers to quickly develop single-page applications because it uses C sharp instead of JavaScript to write the client-side logic.

A challenge that I faced recently while developing a Blazer application was to dynamically add a JavaScript file that was used only in a single component. Blazer allows adding script tags only to the root HTML document. This makes it difficult to add JavaScript files that are required only in a single or few components.

In this post, I'll explain how we can add JavaScript code dynamically to a single component in Blazor.

Add Script To Components

To load a script file in a component, we should first, add a JavaScript function that loads the JavaScript from the specified URL to the main JavaScript file of the project.

The source code of this project can be downloaded from GitHub.

GitHub - mishelshaji/DynamicJavaScriptInBlazor: Dynamically Add JavaScript in Blazor Components
Dynamically Add JavaScript in Blazor Components. Contribute to mishelshaji/DynamicJavaScriptInBlazor development by creating an account on GitHub.

Created a script loader

Add a new function to the script.js file. This function will load a script file from the specified URL.

function loadJs(sourceUrl) {
	if (sourceUrl.Length == 0) {
		console.error("Invalid source URL");

	var tag = document.createElement('script');
	tag.src = sourceUrl;
	tag.type = "text/javascript";

	tag.onload = function () {
		console.log("Script loaded successfully");

	tag.onerror = function () {
		console.error("Failed to load script");


Add this script file to the root document _Host.cshtml. This file will be located in the Shared folder.

/* Add this code above the Blazor server script */
<script src="/js/site.js"></script>
<script src="_framework/blazor.server.js"></script>

Inject IJSRuntime

Go to the Index.razor component, or any other component where you want to load scripts dynamically inject the IJSRuntime.

@inject IJSRuntime _js

Then, override the OnAfterRenderAsync method and call the loadJs function.

protected override async Task OnAfterRenderAsync(bool firstRender)
    var targetUrl = "https://unpkg.com/sweetalert/dist/sweetalert.min.js";
    await _js.InvokeVoidAsync("loadJs", targetUrl);

In this example, we are loading the Sweetalert library from a CDN. You can replace this URL with the URL to your JavaScript code.

Invoke JS Using IJSRuntime

Now, we have loaded a new script file dynamically from the component. Any function from the newly added script can be called with the help of IJSRuntime.

Here's an example.

@page "/"
@inject IJSRuntime _js;

<h1>Hello, world!</h1>

Welcome to your new app.

<button @onclick="Alert">Show Alert</button>

    protected override async Task OnAfterRenderAsync(bool firstRender)
        var targetUrl = "https://unpkg.com/sweetalert/dist/sweetalert.min.js";
        await _js.InvokeVoidAsync("loadJs", targetUrl);


    async Task Alert()
        await _js.InvokeVoidAsync("swal", "Success!", "Script loaded", "success");

I hope this post will help you. Happy coding. If you have any questions, let me know in the comments below.