Primitive Types in JavaScript

 

Key Concepts

Like any other programming language, JavaScript supports multiple data types. Understanding these types and the different operations you can perform on them is essential to coding effectively with JavaScript.

JavaScript Data Types

The data types supported by JavaScript fall into two categories, primitive and object types. In this post, I provide an overview of primitive types and introduce object data types in the next post.

Dynamic Typing

JavaScript is a dynamically typed language. Dynamic typing means that the type of a variable is known at runtime, but not at compile time. Therefore, you do not need to declare the type of your variables. The language interpreter will extract the type of a variable from the value assigned to it at the runtime. This feature makes writing code more flexible, but less error-tolerant. Some errors may only be detected at runtime and not early at compile time.

Primitive Data Types

Primitive data types are the basic blocks for data representation and handling. They are built-in in most programming languages and used to construct more complex data structures. Primitive types are immutable. In other words, their values cannot be changed. There are seven primitive data types in JavaScript, which I present in the second table below with a brief description and examples.

Type Checking

JavaScript provides the ‘typeof’ operator to check the type of a variable.

Type Conversion

JavaScript supports implicit and explicit type conversion, which I explain in the following table.

Type Conversion in JavaScript
Conversion	Definition	Code snippet	Code Output
Implicit	Converting types when necessary	let str = '12' + 8; console.log(str); console.log(typeof(str));	128 string
Explicit	Converting types using functions	let num = Number('475'); console.log(num); console.log(typeof(num));	475 number

Primitive Types

Here is a summary of the primitive types with examples in JavaScript.

Primitive Types in JavaScript
Type	Description	Example	Code Snippet	Code Output	Checking	Checking Output
Number	integer and float numbers	18, 45.5	let exp = 18 * 3 + 45.5; console.log('exp:', exp);	exp: 99.5	console.log(typeof(18));	number
BigInt	large integers	9007199254740991n	let expBI = 9007199254740991n / 30n; console.log('expBI:', expBI);	expBI: 300239975158033n	console.log(typeof(9007199254740991n));	bigint
String	sequence of characters	"nice", 'life'	let str1 = "Hello"; let german_str1 = str1.replaceAll("e", "a"); let str2 = "World!"; let german_str2 = str2.replaceAll("o", "e") .replaceAll("r", "").replaceAll("d", "t") console.log(german_str1 + " " + german_str2);	Hallo Welt!	console.log(typeof("nice"));	string
Boolean	logical values ‘true’ and ‘false’	true	let found = false; let c = "b"; let str = "beautiful dream"; if (str.indexOf(c)>-1){ found = true; } if (found){ console.log(c, "is found in", str); }	b is found in beautiful dream	console.log(typeof(true));	boolean
Undefined	a declared variable to which no value is assigned	let item;	let item; if (item == undefined){ console.log(item); }	undefined	console.log(typeof(undefined));	undefined
Null	no value is provided	let item = null;	let item = null; if (item){ console.log(item); } else { console.log("Your item is null"); }	Your item is null	console.log(typeof(null));	object
Symbol	unique and immutable identifier	let item = Symbol("name");	const sym1 = Symbol(); const sym2 = Symbol("name"); const sym3 = Symbol("name"); console.log(sym1 === sym2); console.log(sym2 === sym3);	false false	console.log(typeof(Symbol("name")));	symbol