Unable to get property 'textbox1' of undefined or null refer

Question

Hello i am trying to transfer data from webform1 to webform2 how to acheive this using javascript and whn i tried i am getting this error ex:"0x800a138f - JavaScript runtime error: Unable to get property 'textbox1' of undefined or null reference"

following is the code which is under button click event.Thanks

ex:

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string strtxtid=datagrid.items[0].cells[1].text.trim();

string strtxtname=datagrid.items[0].cells[2].text.trim();

string strSubject=datagrid.items[0].cells[3].text.trim();

strScript += "<script language=javascript>";

strScript += "window.open.Webform1.textbox1.value='" + strtxtid + "';";

strScript += "window.open.Webform1.textbox2.value='" + strtxtname + "';";

strScript += "window.open.Webform1.textbox3.value='" + strSubject + "';";

strScript += "window.open.__doPostBack('textbox4','');";

strScript += "window.close();";

strScript += "</script>";

Response.Write(strScript);