Onclick javascript-Updating child records or List of records

{!REQUIRESCRIPT("/soap/ajax/30.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/30.0/apex.js")}

try{
	var records = {!GETRECORDIDS($ObjectType.Contact)};
	var SelectedIds='';
	var updatedList = []; //list of contacts to be updated
	var accid;
	if(records.length<1) {
		alert("Please choose at least one contact.");
	}else {
		for(var i=0;i < records.length; i++){
			SelectedIds+="'"+records[i]+"',";
		}
		SelectedIds=SelectedIds.substring(0,SelectedIds.length - 1);
		alert(SelectedIds);
		var project = sforce.connection.query("Select id, Name,AccountId,contact_update_required__c from Contact where id in ("+SelectedIds+")");
		var cons1 = project.getArray("records");
		if(cons1.length){
			for (var n=0; n<cons1.length; n++){
				var sf = new sforce.SObject("Contact");
				sf.id = cons1[n].Id;
				sf.contact_update_required__c=true;
				accid=cons1[n].AccountId;
				updatedList.push(sf);
			}
			var result = sforce.connection.update(updatedList);
			if (result[0].success == 'true'){
				alert('Records updated successfully');
				window.location.href = '/'+accid;
			}else{
				alert('An error has occoured. Error: '+result[0].errors.message);
				window.location.href = '/'+accid ;
			}
		}
	}

}catch(e){
	alert('some system error occured. Please try later');
}