Using JavaScript Interop in Blazor Applications

Introduction:

Blazor is an open-source web framework for building web applications using .NET and C#. It allows developers to create web applications with a rich user interface using a combination of HTML, CSS, and C#. Sometimes, we may need to use JavaScript in our Blazor applications to access browser-specific functionality or interact with third-party libraries. In this how-to guide, we will explore how to use JavaScript interop in Blazor applications to call JavaScript functions from C# code.

To use JavaScript interop in a Blazor application, we need to create a JavaScript file that contains the functions we want to call from C# code. Create a new JavaScript file in the "wwwroot" folder of your project and add the following code:

This code defines a function named "showAlert" that displays an alert dialog with the specified message.

Once we have created the JavaScript file, we need to add it to our Blazor application. In the main page of our application, add the following code to include the JavaScript file:

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

This code will include the "example.js" file in our application and make the functions defined in the file available for use in our C# code.

Step 3: Define a JavaScript interop method in C# code

To call a JavaScript function from C# code, we need to define a JavaScript interop method in our C# code. Add the following code to a C# class in your application:

csharp

[JSInvokable]

public static void ShowAlert(string message)

{

  JSRuntime.Current.InvokeAsync<object>("showAlert", message);

}

This code defines a static method named "ShowAlert" that is decorated with the "JSInvokable" attribute. The method takes a string argument named "message" and calls the "showAlert" function defined in the JavaScript file.

Step 4: Call the JavaScript interop method from C# code

Now that we have defined the JavaScript interop method in our C# code, we can call it from our Blazor components. Add the following code to a Blazor component

Less

<button @onclick="@(() => ShowAlert("Hello, world!"))">Show alert</button>

This code adds a button to the component that calls the "ShowAlert" method when clicked. The method displays an alert dialog with the message "Hello, world!".

Use case:

Let's say we want to use the Google Maps JavaScript API in our Blazor application to display a map. By using JavaScript interop, we can call the functions provided by the Google Maps API from our C# code.

For example, we can create a component that displays a map and adds a marker to the map at a specified location. We can define a JavaScript interop method named "AddMarker" that takes a latitude and longitude as arguments and calls the "addMarker" function provided by the Google Maps API. Here's an example of what the C# code might look like:

csharp

[JSInvokable]

public static void AddMarker(double lat, double lng)

{

  JSRuntime.Current.InvokeAsync<object>("addMarker", lat, lng);

}

This code defines a static method named "AddMarker" that takes two double arguments named "lat" and "lng". The method calls the "addMarker" function provided by the Google Maps API with the specified latitude and longitude.

Conclusion:

Using JavaScript interop in Blazor applications allows us to call JavaScript functions from C# code and access browser-specific functionality or interact with third-party libraries. In this how-to guide, we explored how to use JavaScript interop in Blazor applications to call JavaScript functions from C# code.

We saw how to create a JavaScript file with functions, add the file to the application, define a JavaScript interop method in C# code, and call the method from a Blazor component. We also saw a use case for JavaScript interop, where we can use the Google Maps JavaScript API to display a map and add a marker to the map at a specified location.

It's important to note that using JavaScript interop in Blazor applications can introduce security risks, as we are effectively allowing C# code to execute JavaScript code in the browser. It's important to validate input and ensure that the JavaScript code being executed is safe and trustworthy.

However, when used properly, JavaScript interop can be a powerful tool for enhancing the functionality of Blazor applications.

We hope you found this guide on Using JavaScript Interop in Blazor Applications insightful and valuable. You can learn more on JBI's Blazor training courses.

Go here if you would like to see the ASP.Net Core Blazor Official Documentation.