substring of php var inside javascript

Question

i am trying to use the substring method inside a Js code wich echoes some php variable but it does not work.

$('#tarif_public_total').val( <?php echo $_tarif_public; ?> * $('#tarif_public').val() )

u=$('#tarif_membre').val()* <?php echo $_tarif_membre; ?> + $('#tarif_public').val()* <?php echo $_tarif_public; ?>
uu=u.substring(0,6)

$('#total_total').val(uu)

what im doing wrong here?

Answer 1

After using parseInt() on all the instances of val() (like Gert G suggested) you have to do:

uu=("" + u).substring(0,6)

or:

uu=String(u).substring(0,6)

Since you can't use substring on numbers. You have to cast back to a string using ("" + var)

Live demo of ("" + var)