Use Luci js API return value on js array

Hi all,

Can anyone know use luci js api return value on js array ?
Below is my source code write on js file, but on luci webgui it show object Promise on the show field.

Example :

var wan_mac = new Promise(function geet_wan_mac() {
     return fs.exec('ifconfig wan | grep HWaddr | awk \'{print $5}\'');

var fields = [
_('Local Time'), datestr,
 _('WAN MAC Address'), wan_mac

Thanks for your help!

I just use rpc method to add iterm below is my reference website.

But I still don't understand how use luci js api : fs.exec to get result output and show on js array as promise object.

Hope someone can explain and tell a example how to do it.