Because of this prototypal system, all custom objects are created inline in a given script. Custom JS objects are primarily created through what is called a literal notation, they are ‘literally’ written out line-by-line in the script and are ‘literally’ built in memory as the script executes line-by-line.
Mutable Key/Value Collections
JS Objects are always passed by reference, meaning as an object is passed from function to function or throughout a script it is only its reference in memory that is being passed around not the actual object. This also means that the object is also not being copied or duplicated in any way as it is being passed around.