Ajax Callback application process and its usage In Oracle APEX 

Ajax Callback/ On-Demand: Run this application process when requested by page Process.

If you create an Ajax Callback/On-Demand process that dynamically shows the values of another item without submitting the page.

To create an application process :
  1. Navigate to the Shared Components page:
  2. Under Application Logic, select Application Processes
  3. Click on create button.

Name – Enter a name for the application process. In my Case GET_NAME
Sequence – 1
Point – Ajax Callback/ On-Demand Run this application process when requested by page Process.
Click Next Button

declare
    v_ename varchar2(100);
begin
   select 
          ename into v_ename 
   from 
          emp 
   where 
          empno = APEX_APPLICATION.g_x01;
HTP.P(v_ename);

exception when others then 
null;
end;

Create a normal page with a two-page item and paste the below code in Function and Global Variable Declaration.

function get_name() {

  apex.server.process("GET_NAME", {
    x01: $v('P1_ID')
  }, {

    dataType: 'text',
    success: function(pData) {
      $s('P1_NAME', pData);
    }
  });

We can call the above-written function in many ways like using dynamic action or directly in the custom attribute.

You might like: