How can I prevent my page from reloading after the "alert?"

Here's my code:

$workqueueroleassigncheck = cer_workqueueroleassigncheck($tmp_entity[$i]["entityid"], $EntityID, $tmp_user[$k]["userid"]);
					if($workqueueroleassigncheck["count"]>0)
					{
					print '<script type="text/javascript">'; 
					print 'alert("be careful not to assign a role to the same person twice...!")'; 
					print '</script>';  
					}
					else
					{
					$workqueueroleassignsave = cer_workqueueentityassignsave($tmp_role[$j]["roleid"],$tmp_entity[$i]["entityid"],$EntityID, $tmp_user[$k]["userid"], $updateuserid);
					}

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Basically, if the user attempts to add a record that's a duplicate of what's already in place, they get an alert and the insert code doesn't fire.

Problem is, I don't want the page to reload. Is there a way to structure my code where the checkboxes that had been checked remain so rather than the page reloading?