Script not running in google chrome - asp.net

Question

I have a page in aspx which uses the following code. The issue is that it fetches the values from SQL and put into boxes using internet explorer but not doing using chrome
var element = document.getElementById("ctl00$pagecontent$Flexibleselect_Reol$ctl01");
//alert(element);
//alert('<%=Flexibleselect_Reol.Controls[1].ClientID %>');
element.onchange = (function(onchange) {
return function(evt) {
// reference to event to pass argument properly
evt = evt || event;
// new code "injection"
var puselectobj = document.getElementById('ctl00$pagecontent$Flexibleselect_Reol$ctl01');
var paramVal = puselectobj.value;
// alert(paramVal);
var newUrl = updateURLParameter('ProcessUnit', paramVal);
theForm.action = newUrl;
if (onchange) {
onchange(evt);
}
}
})(element.onchange);
// alert(element.onchange);
function updateURLParameter(param, value) {
var url = theForm.action;
var newAdditionalURL = "";
var tempArray = url.split("?");
var baseURL = tempArray[0];
var additionalURL = tempArray[1];
var temp = "";
if (additionalURL) {
tempArray = additionalURL.split("&");
for (i = 0; i < tempArray.length; i++) {
if (tempArray[i].split('=')[0] != param) {
newAdditionalURL += temp + tempArray[i];
temp = "&";
}
}
}
var paramVal = value;
var rows_txt = temp + "" + param + "=" + paramVal;
var querystr = "?" + newAdditionalURL + rows_txt;
return baseURL + querystr;
}
I am getting the following error when running in chrome
"Uncaught TypeError: Cannot read properties of null (reading 'onchange')"