using System;

using System.Text;

using System.IO;

using HtmlAgilityPack;

public class Program

{

    public static void Main()

    {

        HtmlDocument doc = new HtmlDocument();

        doc.LoadHtml("<script></script>");

        string script = "'use strict';\r\n\r\nmodule.exports = somevariable;";

        var scriptNode = doc.DocumentNode.ChildNodes.FindFirst("script");

        HtmlTextNode textNode = doc.CreateTextNode(script);

        scriptNode.AppendChild(textNode);

        StringBuilder builder = new StringBuilder();

        using (var writer = new StringWriter(builder))

        {

            doc.Save(writer);

        }       

        Console.WriteLine(builder.ToString());

    }

}