I need to select document.referrer with webdriverio using javascript to test previous page URL using Mocha.

Tried:

const previousPage = await $('document') 
console.log(await previousPage.referrer);
//returner undefined

and

const previousPage = await browser.$('document') 
console.log(await previousPage.referrer);
//returner undefined

I can't figure out what I am doing wrong!