function pageLoad() {
        log.debug('pageLoad');
    
        var ele = document.getElementById('TextBox1');
        var raiseServerEvent = ele.onchange;
        
        ele.onchange = function(e) { 
            log.debug('Before TextBox1_Change');                        
            TextBox1_Change(ele, raiseServerEvent, e || event);
        }      
    }    
       
    function TextBox1_Change(sender, raiseServerEvent, e) {
        log.debug('TextBox1_Change');
        
        if (sender.value == 'server') {
            raiseServerEvent();
            log.debug(raiseServerEvent);            
        }
    }       
    
    function TextBox1_InlineChange() {
        var ele = document.getElementById('CheckBox1');
        log.debug('TextBox1_InlineChange: return ' + ele.checked);        
        return ele.checked;
    }   

<asp:TextBox ID="TextBox1" runat="server" 
    AutoPostBack="True" 
    OnChange="if (!TextBox1_InlineChange()) return;"
    OnTextChanged="TextBox1_TextChanged">
</asp:TextBox>
<asp:CheckBox ID="CheckBox1" runat="server" Text="AutoPostback" />