asp.net core tag helper for conditionally add class to an element

Question

In Asp.Net MVC we can add class conditionally as following code:

Answer 1

There's no default way to do what you're asking. You would have to write a TagHelper that did that logic for you. Aka

[HtmlTargetElement(Attributes = "asp-active")]
public class FooTagHelper : TagHelper
{
    [HtmlAttributeName("asp-active")]
    public bool Active { get; set; }

    public override void Process(TagHelperOutput output, TagHelperContext context)
    {
        if (Active)
        {
            // Merge your active class attribute onto "output"'s attributes.
        }
    }
}

And then the HTML would look like: