Modify javascript

I need a function instead returning "'[object Promise]" to return actual value of function.
From: https://gist.github.com/wilsonpage/01d2eb139959c79e0d9a
This is the function:
Storage.prototype.get = function(key) {
return this.ready.then(() => {
return new Promise((resolve, reject) => {
var request = this.getStore().get(key);
request.onsuccess = e => resolve(e.target.result);
request.onerror = reject;
});
});
};