Cypress+Firestore=invalid data

Function DocumentReference.set() called with invalid data. Data must be an object, but it was: a custom Object object

not work

firebase.firestore().collection("foo").doc("bar").set({})

hacks also don't work

Object.assign({}, obj)

JSON.parse(JSON.stringify(obj))

correct insight

This is likely a cross-window issue: GWT code runs in an iframe; if Firebase is looking for a "bare object", it likely compares the object's constructor, which won't be the expected one if the object crosses the iframe boundary.

Cypress also uses iframes. So we can't store objects created in testcases.