SAP BSP to auto select region when user selects country using HTML and Javascript

types: begin of t_region,
  regionid(4) type c,
  text        type string,
 end of t_region.
types: tt_region type STANDARD TABLE OF t_region.
types: begin of t_country,
  land1           type land1,
  landx           type landx,
  regionid(4)     type c,
  text            type string,
 end of t_country.
types: tt_country type STANDARD TABLE OF t_country.

* Select Country Dropdown Values from SAP country table
SELECT *
  FROM t005t
  INTO CORRESPONDING FIELDS OF TABLE it_country
 WHERE spras EQ 'EN'.
SORT it_country BY landx.
********************
*Build region table*
********************
* Creates an entrty for each region code, you can create as many of these
* as you want but should really be stored in a SAP Ztable oince you understand
* how it works
wa_region-regionid = 'EU'.
wa_region-text         = 'Europe - EU'.
APPEND wa_region to it_region.
wa_region-regionid = 'ROTW'.
wa_region-text         = 'Rest of the World'.
APPEND wa_region to it_region.
wa_region-regionid = 'UK'.
wa_region-text         = 'United Kingdom'.
APPEND wa_region to it_region.
wa_region-regionid = 'ASIA'.
wa_region-text         = 'Asia'.
APPEND wa_region to it_region.
***
************************
*Link Country to region*
************************
loop at it_country into wa_country.
* The following only assigns a few countries as this should really be stored in a
* SAP Ztable. Others are then simply assigned to the ROTW id
  case wa_country-land1.
    when 'GB'.
       wa_country-regionid  = 'UK'.
    when 'FR'.
       wa_country-regionid  = 'EU'.
    when 'GR'.
       wa_country-regionid  = 'EU'.
    when 'US'.
       wa_country-regionid  = 'ROTW'.
    when 'ZA'.
       wa_country-regionid  = 'ROTW'.
    when 'HK'.
       wa_country-regionid  = 'AISA'.
    when others.
       wa_country-regionid  = 'ROTW'.
  endcase.
  MODIFY it_country from wa_country.
endloop.
***