* Mix properties into target object.

* Make a map and return a function for checking if a key * is in that map.

* Quick object check - this is primarily used to tell * Objects from primitive values when we know the value * is a JSON-compliant type.

* Create a cached version of a pure function.

* Attempt to create an observer instance for a value, * returns the new observer if successfully observed, * or the existing observer if the value a

* Remove an item from an array

* Check if value is primitive