Why do object keys get mixed up?

Question

JavaScript

I created two objects

const obj1 = {
     userId: 2
}
const obj2 = {
      userId: 1
}

Created two recursive timeouts for these two objects, these are different functions. And then I go through for in on the keys of the object. But sometimes the key from obj1 gets into the function that checks obj2, why is this happening?