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4.8 The Big Picture

Data and Structure Types

JavaScript has 9 standard types categorized as follows:

  1. Data Types (primitives): undefined, Boolean, Number, String, BigInt, and Symbol.
  2. Structural Types (objects): Object, Array, Map, Set, WeakMap, WeakSet, Date, and Function.
  3. Structure Root Primitive: null.

Function : a non-data structure

Note

Functions are considered a non-data structure in JavaScript. However, they are objects.

Note

Do not worry if you do not know every type listed above. We will explain it at the right time.

Primitive types

Primitive Types have no properties or methods. Their values are immutable; they can not be changed. You can check the type of primitive type using typeOf primitive.

To access a property or apply a method on a primitive type, The JavaScript engine converts the primitive to its respective object. It accesses the property or applies the method, then it converts the primitive object to its original primitive value.

Primitive Type Respective Object Constructor
string String String()
boolean Boolean Boolean()
number Number Number()
bigInt BigInt BigInt()

You get primitive value of an object using object.valueOf().

Objects

An object is a collection of properties. You can create objects with the literal notation {}. You can also construct an object using the Object constructor and the keyword new. For instance; new Object().

Built-in Objects

Date, Array, and Function are examples of JavaScript built-in objects.

Every object is constructed using a constructor.

Here is a list of built-in objects and their respective constructors:

Built-in Object Constructor Object Instance
Object Object() new Object()
Date Date() new Date()
Array Array() new Array()
Function Function() new Function()
String String() new String()
Number Number() new Number()
Boolean Boolean() new Boolean()

Structure Root Primitive

null is a built-in JavaScript object. Its value is primitive because it has similar primitive behavior. However, null is an object and every object is derived from it.

typeof null === "object" // true