Null, Undefined and Symbol

Null, undefined, and Symbols are primitive types.

Null

Null represents an intentional absence of a primitive or composite value of a defined variable.

Undefined

Undefined represents that a value is not defined.

Symbol

A Symbol() is a unique value without an associated literal value. They are useful as unique keys, because Symbol() == Symbol() is false. At this stage, just accept that symbols exist. You don’t have to use them for anything yet.