How to get dynamic control checkbox in client side?

In .net server side i was creating Dynamic controls text-box,checkbox. If i click the checkbox inside all the checkbox list controls it should get checked. refer this image.

server side using new EventHandler i can achieve this.But i want this in clientside.

Clientside code :

function CheckboxHeaderClick1() {

    var chkBox = "<%=strchx1ID %>";
    if (chkBox.checked) {
        var checkboxList = "<%=strchxboxlist1ID %>"; 
        var chkBoxCount = "<%=strchxboxlist1Count %>";
        for (var i = 0; i < chkBoxCount.length; i++) {
            chkBoxCount[i].checked = true;
        }
    }
    else {
        var checkboxList = "<%=strchxboxlist1ID %>"; 
        var chkBoxCount = "<%=strchxboxlist1Count %>";
        for (var i = 0; i < chkBoxCount.length; i++) {
            chkBoxCount[i].checked = false;
        }
    }
}

but chkBox.checked is coming undefined.From server side to client side how i can pass the checkbox control?

enter image description here

enter image description here

My code :

  System.Web.UI.WebControls.Label lbllookup = new System.Web.UI.WebControls.Label();
                                                            Panel pnl1 = new Panel();

                                                                    chx1 = new CheckBox();
                                                                chx1.ID = "chx" + fieldname;
                                                                strchx1ID = chx1.ClientID;
                                                             //   chx1.AutoPostBack = true;
                                                                if (!IsPostBack)
                                                                    chx1.Checked = true;
                                                               // chx1.CheckedChanged += new EventHandler(this.chx1_CheckedChanged);
                                                               // chx1.Attributes.Add("onclick", "CheckboxHeaderClick1();");
                                                                chx1.Attributes.Add("onclick", "javascript:CheckboxHeaderClick1();return false;");
                                                                checkboxID = chx1.ID;
                                                                chx1.Style.Add(HtmlTextWriterStyle.BackgroundColor, "#f2f2f2");
                                                                chx1.Style.Add(HtmlTextWriterStyle.Color, "#287082");

                                                                chx1.Style.Add(HtmlTextWriterStyle.PaddingBottom, "6px");

                                                                chx1.Style.Add(HtmlTextWriterStyle.FontSize, "14px!important;");
                                                                pnl_filters.Controls.Add(chx1);
                                                                lookupfieldcount++;
                                                                chxboxlist1 = new CheckBoxList();
                                                                chxboxlist1.ID = fieldname;
                                                                strchxboxlist1ID = chxboxlist1.ClientID;

//chx1.CheckedChanged += new EventHandler(this.chx1_CheckedChanged);                                                                 lbllookup.Text = field.Title;
                                                                lbllookup.Style.Add(HtmlTextWriterStyle.BackgroundColor, "#f2f2f2");
                                                                lbllookup.Style.Add(HtmlTextWriterStyle.Color, "#287082");
                                                                //lbllookup.Style.Add(HtmlTextWriterStyle.PaddingLeft, "8px");
                                                                //lbllookup.Style.Add(HtmlTextWriterStyle.PaddingTop, "4px");
                                                                lbllookup.Style.Add(HtmlTextWriterStyle.PaddingBottom, "6px");
                                                                //  lbllookup.Style.Add(HtmlTextWriterStyle.PaddingRight, "142px");
                                                                lbllookup.Style.Add(HtmlTextWriterStyle.FontSize, "14px!important;");
                                                                lbllookup.Style.Add(HtmlTextWriterStyle.Width, "240px");
                                                                pnl_filters.Controls.Add(lbllookup);


                                                                pnl1.ID = "pnl" + fieldname;
                                                                if (chxboxlist1.Height == 105)
                                                                {
                                                                    pnl1.Style.Add(HtmlTextWriterStyle.Height, "105px");
                                                                    pnl1.Style.Add(HtmlTextWriterStyle.OverflowY, "scroll");
                                                                }
                                                                else
                                                                {
                                                                    pnl1.Style.Add(HtmlTextWriterStyle.Height, "90px");
                                                                }
                                                                pnl_filters.Controls.Add(pnl1);
                                                                pnl1.Controls.Add(chxboxlist1);

                                                                if (!IsPostBack)
                                                                    bind_Fields(fieldname, listtitle, lookupfield, chxboxlist1);
                                                                if (chxboxlist1.Items.Count == 0)
                                                                    bind_Fields(fieldname, listtitle, lookupfield, chxboxlist1);
                                                                checkboxcount++;