Webmethod called but not entering success/error response in javascript

I have a WebForms project and I have 1 page with a Datatable inside. The relevant things are organized in this way:
Site.master:

<body>    
  <form runat="server">    
    <asp:ScriptManager runat="server" EnablePageMethods="true" ID="ScriptManager1">    
      <Scripts>    
          <asp:ScriptReference Path="~/Scripts/custom-datatable.js" />

The WebMethod in Default.aspx.cs:

    [System.Web.Services.WebMethod]
    public static object GetAllCONTEGGI(Nullable<DateTime> dateFrom, Nullable<DateTime> dateTo, Nullable<int> idUtente, Nullable<int> eventType, Nullable<int> logType)
    {
...
        var result = LogReader.SearchLogEvento(dateFrom, dateTo, idUtente, string_eventType, string_logType);
        return result;
    }

The javascript custom-datatable.js:

$(document).ready(function () {
...
PageMethods.GetAllCONTEGGI(null, null, null, null, null, SuccessOnLoadingLoadUtentiFunzioni, OnError);
function SuccessOnLoadingLoadUtentiFunzioni(dataset){...}
function OnError(data) { }
}

The Default.aspx page:

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
    ...
    <table id="tblConteggi" class="display">
    ...
    <button id="btnClick" <%-- onclick="LoadDataTable();"--%> >Cerca log</button>
    ...

This way works fine, i.e. calling all the javascript code inside $(document).ready(function () { ...

I noted that, when clicking the button id="btnClick", the page does a postback, as I see when i set a breakpoint in
protected void Page_Load(object sender, EventArgs e) { ... of Default.aspx.cs

Anyways, the PageMethod call is passed to SuccessOnLoadingLoadUtentiFunzioni when I create/load the Datatable.

What is strange for me, is that, when I add the onclick event handler in the button <button id="btnClick" onclick="LoadDataTable();" >Cerca log</button>, and insert all the javascript code inside that event, and not in document.ready:

LoadDataTable()
{
...
PageMethods.GetAllCONTEGGI(null, null, null, null, null, SuccessOnLoadingLoadUtentiFunzioni, OnError);
function SuccessOnLoadingLoadUtentiFunzioni(dataset){...}
function OnError(data) { }
}

, the WebMethod is called (as I see in debug), but then it doesn't pass neither through OnSuccess (SuccessOnLoadingLoadUtentiFunzioni), nor through OnError.

My questions are: 1. Aren't WebMethods supposed not to make postbacks ? 2. What causes the WebMethod not to return the response in the second case (the case when I insert the javascript code in a function and not directly in document.ready)

Thanks

Solution

Riplace with this:

<button id="btnClick" type="button" onclick="LoadDataTable();" >Cerca log</button>

You are missing type="button", this will prevent the page to postback, and will allow the response to pass to OnSuccess