Add the following java script code in page load of the entity
getAlertForAddExistingAccountButton = function(lookupUrl) {
var iframe = crmForm.all.IFRAME_Accounts; // IFRAME_Accounts ID
var crmGrid = iframe.contentWindow.document.all['crmGrid'];
// If it's not N:N lookup dialog, we skip it.
if (lookupUrl.toLowerCase().match(/\/_controls\/lookup\/lookupmulti.aspx/i) == null)
return lookupUrl;
// If the lookup window is not concerned with the entity that we are interested in, we skip as well
if (GetQueryString(lookupUrl, 'objecttypes') !== crmGrid.GetParameter('otc'))
return lookupUrl;
return lookupUrl;
};
(function replaceCrmLookups() {
window.oldOpenStdDlg = window.oldOpenStdDlg || window.openStdDlg;
window.openStdDlg = function() {
var cnf = confirm("Are you sure to open Account lookup? ");
if(!cnf)
return;
arguments[0] = getAlertForAddExistingAccountButton(arguments[0]);
return oldOpenStdDlg.apply(this, arguments);
};
})();
Now you will get confirm alert on add existing button click before opening the account lookup page.