Data types

Types in javascript

JavaScript has several primitive data types, which are the basic types of data that can be directly operated on. They include:

Name	Description	Example
String	Represents textual data	"The Great Gatsby"
Number	Represents both integer and floating-point numbers	2023, 19.99
Boolean	Represents a logical entity having two values	true, false
Undefined	Represents a variable that has not been assigned a value	undefined
Null	Represents the intentional absence of any object value	null
BigInt	Represents integers with arbitrary precision, useful for very large numbers	9007199254740992n

Checking the type

We can check the type of a variable using the typeof keyword.

js

const pageCount = 210
const ISBN = '978-3-16-148410-0'
const premiumMember = true

console.log(typeof pageCount)
console.log(typeof ISBN)
console.log(typeof premiumMember)

output

number
string
boolean

Adding strings

If we have two string types, when we add them, they get concatenated (glued together).

js

let author = 'Toni Morrison'
let title = 'Beloved'

console.log(title + ' was written by ' + author)

output

Beloved was written by Toni Morrison

Changing type

In some cases, it is possible to change from one type to another.

let bookCount = String(100) // Converts number to string
let price = Number('19.99') // Converts string to number

Type coercion

We need to be careful when operating on values of different types.

js

const price1 = '10'
const price2 = 5
const totalPrice = price1 + price2

console.log(totalPrice) // oops!

output

105