ASP.NET Core MVC Interview Question #166

What is a custom Tag Helper?

Testing, AJAX/JavaScript Integration, Localization & Advanced MVC Senior Advanced

Quick Interview Answer

A custom Tag Helper is a server-side component that participates in rendering selected HTML elements or custom tag-like markup in Razor. It can inspect attributes, modify output, or generate reusable presentation behavior.

Detailed Explanation

A custom Tag Helper is a server-side component that participates in rendering selected HTML elements or custom tag-like markup in Razor. It can inspect attributes, modify output, or generate reusable presentation behavior.

Custom Tag Helpers are useful when a project repeatedly applies the same HTML-generation convention. They should remain presentation-focused and should not hide substantial business workflows.

Code Example

[HtmlTargetElement("email-link")]
public class EmailLinkTagHelper : TagHelper
{
    public string Address { get; set; } = string.Empty;

    public override void Process(
        TagHelperContext context,
        TagHelperOutput output)
    {
        output.TagName = "a";
        output.Attributes.SetAttribute(
            "href", $"mailto:{Address}");
        output.Content.SetContent(Address);
    }
}