Data Types in JavaScript

In JavaScript, a primitive (primitive value, primitive data type) is data that is not an object and has no methods or properties. There are 7 primitive data types:

string, number, bigint, boolean, undefined, symbol and null

All primitives are immutable. It is important not to confuse a primitive itself with a variable assigned a primitive value. It is important not to confuse a primitive itself with a variable assigned a primitive value.

tip

All primitive types, except null, can be tested by the typeof operator, because typeof null returns object, so one has to use === null to test for null.

All primitive types, except null and undefined, have their corresponding object wrapper types, which provide useful methods for working with the primitive values. For example, the Number object (object wrapper of number) provides methods like toExponential(). When a property is accessed on a primitive value, JavaScript automatically wraps the value into the corresponding wrapper object and accesses the property on the object instead. However, accessing a property on null or undefined throws a TypeError exception.

Type	typeof return value	Object wrapper
null	object	N/A
undefined	undefined	N/A
number	number	Number
bigint	bigint	BigInt
boolean	boolean	Boolean
string	string	String
symbol	symbol	Symbol

• The typeof operator in JavaScript returns a string indicating the type of the operand's value. All primitive types, except null will return the same data type. Others will return either object (Array, and Date included) and function.

• Note that the typeof operator returns object for arrays, null and functions. This is because arrays are objects in JavaScript, and null and function are special types of objects.

Here are some examples of how to use the typeof operator:

typeof 1; // returns 'number'
typeof 37n; // returns 'bigint'
typeof 'hello'; // returns 'string'
typeof true; // returns 'boolean'
typeof undefined; // returns 'undefined'
typeof null; // returns 'object'
typeof []; // returns 'object'
typeof function() {}; // returns 'function'
typeof Date; // returns 'function'
typeof new Date();  // returns 'object'
typeof Object; // returns 'function'
typeof new Object(); // returns 'object'

function is a Function object and object(with small cap) is an Object object. So both are object only. Object (with capital 'O') is just a constructor function.

A function is an instance of Function, so that makes a function an object. i.e, Function constructs an object which is a function.