I just figured out how to add JavaScript TextBox Character Count functionality to my module with minimal code, and I thought I would give it to the community. You will need to place code in your control and codebehind. I hope this helps some of you module developers out there. Let me know if you need help.

ascx control:

<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder><br />
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

codebehind (Page_Load):

if(!IsPostBack)
{
 String scriptText = "";
 scriptText += "function DisplayCharCount(){";
 scriptText += "   spanCounter.innerText = " + " document.forms[0]." + TextBox1.ClientID + ".value.length";
 scriptText += "}";
 Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "CounterScript", scriptText, true);
 TextBox1.Attributes.Add("onkeyup", "DisplayCharCount()");
 LiteralControl spanLiteral = new LiteralControl("<span id=\"spanCounter\"></span>");
 PlaceHolder1.Controls.Add(spanLiteral);
}