[object Object] is the default string representation of a JavaScript Object.
I would understand if it was just [Object] or [object], but why [object Object]? Why the first word is lowercase and the second one is uppercase? Is it part of JSON or JavaScript?
All objects have a toString method that displays something in the format [object type], where type is the object type.
When called on null you get [object Null] and when called on an object you get the string [object Object] because it's based on the Object constructor (capital "O"), that's why it says object twice, it's an object of the type Object.
JSON is a lightweight data-interchange format, and doesn't really have anything to do with JavaScript other than being named "JavaScript Object Notation" because it's written like a JavaScript object.
