Как вернуть значение из Promise у Javascript?

'use strict';

const VKapi = require('node-vkapi');
var urlencode = require('urlencode');
var _ = require('underscore');
 
const VK = new VKapi({
  token: 'a89e24c414d82ba1a3fad33989f833339dsdb6db615004dfa01de61f73cac48eabdff34e4e8bf846e1a2f'
});

var start = function(user_id) {
  VK.call('groups.get', {
	  user_id: user_id,
	})
  .catch(e => {console.log(e)});
}

var b;
var a = start(343910101).then(res => {b = res});
console.log(b);

C:\Users\Общий\Desktop\vks>node gtp.js
undefined