How to use isMemberOf function in client script ServiceNow?

Step 1: Create a display Business rule with below Script

g_scratchpad.group = gs.getUser().isMemberOf('GROUP NAME');

Step 2:

Write onLoad client script

function onLoad() {
 if (g_scratchpad.group){
g_form.setValue('description', 'User exist in group');
 }
  }