Data Types

A variable in JavaScript can contain any data.
It is possible to assign a string to a variable initially and then reassign the variable to a number.
A programming language that has this capability is called 'Dynamically Typed'

Data Type	Value or Reference	Comments
string	Value Type	is Immutable and cannot be changed once they have been created
number	Value Type	is Immutable and cannot be changed once they have been created (float) Prone to rounding errors
bigint	Value Type
boolean	Value Type
symbol	Value Type	Added in ES 2015
null	Value Type
undefined	Value Type

object	Reference Type	is Mutable and can be changed once it has been created
function	Reference Type	is Mutable and can be changed once it has been created

function Data Type

A 'function' data type is a special type of object.

typeof function() {} // "function" 
typeof new Function    // "function"

array Data Type

An 'array' data type is a special type of object.
It does have some additional properties and functions that a normal object does not have.

typeof myArray            // "object"

Arrays

null evaluates to False in a boolean expression
undefined evaluates to False in a boolean expression
primitive data types are equal if the values match