Webdriverio: access to window object

I'm trying Webdriverio Testrunner with Selenium Standalone. One test I would like to do should check a global variable (window.myVar) but when I try to return the window object I receive something weird

it('should return window', (done) => {

const url = 'http://www.example.com';

browser.url(url);
browser.waitForVisible('body', 20000);
browser.pause(1000);
browser.execute(getWindow)
    .then(result => {
        console.log(result);
    });

});

This print:

․{ sessionId: '6f0cd910-2ec8-11e8-80fb-bf4604ec860e',
  status: 0,
  value: { WINDOW: ':wdc:1521829902692' } }

What is WINDOW: ':wdc:1521829902692'? How can I get the actual window object?