Typeahead TypeError: it.toLowerCase is not a function

as what i can see from your console.log(). you get this.

[{"Outlet":"K-AR3"},{"Outlet":"K-AR4"},{"Outlet":"K-ARN2"},{"Outlet":"K-ARN3"}]

you only need

[{"K-AR3"},{"K-AR4"},{"K-ARN2"},{"K-ARN3"}]

so try to change your controller to

function outletlists()
    {
        extract(populateform());
        $hasil = $this->modelmodel->showdata("SELECT Outlet from transaksi where outlet like '%".$outlets."%'  group by Outlet");
        $data = array();
        foreach ($hasil as $hsl)
            {
                $data[] = $hsl->Outlet;
            }
        echo json_encode($data);
    }