How to correct run WCF services from javascript?

This is my page code:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="ProductType.aspx.cs" Inherits="Application.ProductType" MasterPageFile="~/Main.Master" %>
<asp:Content ID="Content1" ContentPlaceHolderID="MainContentPlaceHolder" runat="server">             
    <script type="text/javascript">
        function getMainTable() { return document.getElementById("<%= ProductGridMain.ClientID %>"); }          
    </script>
    <script type="text/javascript" src="JavaScripts/ProductType.js"></script>
    <asp:ScriptManager ID="ScriptManager1" runat="server">            
            <Services>
                <asp:ServiceReference Path="~/Services/ProductTypeService.svc" />
            </Services>
    </asp:ScriptManager>        
    <asp:Label ID="ProductGridMain" runat="server" Text="Label"></asp:Label>        
    <br />
    <asp:Button ID="AddNewItemBtn" CssClass="Btn" runat="server" Text="New" OnClientClick="NewAddBtn(); return false;" />    
</asp:Content> 

This is the ProductType.js file:

$(document).ready(function() {
    var counter = "fast";
    ProductTypeService.GetMainGridProductTypeHtml(counter, ResultLoadTableMainGridHtml, ErrorLoadTableMainGridHtml);      
});
function ResultLoadTableMainGridHtml(html) {
    //debugger;      
        var tblMainGrid = getMa开发者_高级运维inTable();
        if (tblMainGrid != null && html != null && html != "null" && html != "" && html != " ") {           
            tblMainGrid.innerHTML = html;
        }
}
function ErrorLoadTableMainGridHtml(html) {    
    alert("Error");
}
function NewAddBtn() {
    //debugger;
    var counter = "test";
    ProductTypeService.GetMainGridProductTypeHtml(counter, ResultLoadTableMainGridHtml, ErrorLoadTableMainGridHtml);
}    

The service method returns html code of main grid, then in javascript I insert it into label. When I click on button everything works correctly like I suppose, but page is reloading. How do I call the service method on button click without page reloading?

Why not use HTML button instead of ASP.NET button - that way you can indicate that you don't need submit behavior. For example,

<input type="button" id="AddNewItemBtn" class="Btn" runat="server" value="New" onclick="NewAddBtn()" />

You may eliminate runat="server" if you don't need to refer to the button in the server code.