An Object is a Closure
We know what a closure is. It's a function that gets a little bubble of data pinned to it at runtime, which it can then make use of wherever it goes.
If we really want to shorten this explanation down, we might say that a closure is a bit of behavior tied to a bit of data. As it happens, this is very similar to how objects were described to me when I was first learning object-oriented programming. In his book "Object-Oriented Analysis and Design with Applications", Grady Booch says that "an object is an entity that has state, behavior, and identity." Most other things that an object is are derived from these attributes. Identity is just bonus for our purposes, but in JavaScript at least, it also happens to be true of functions.
“An object is an entity that has state, [and] behavior...”
Now lets squint a little at that object. Focus on some things and let others fade into the background. For example, lets imagine an object with just one public member function. And then, imagine it also has no public properties or fields. It does have some private fields, though. And those private fields are initialized by the constructor of the object's type.
So now what do we have here? A member function, with a little bubble of data pinned to its object at runtime via the constructor function, which it can then make use of wherever it goes.
Sounds familiar.