If block TagHelper

AspIfTagHelper.cs

[HtmlTargetElement("*", Attributes = "[asp-if]")]
public class IfTagHelper : TagHelper
{
    /// <summary>
    /// Shows the element when this condition is true
    /// </summary>
    [HtmlAttributeName("asp-if")]
    public bool IsTrue { get; set; } = true;

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        if (!IsTrue)
        {
            output.TagName = null;
            output.Content.Clear();
        }
    }
}