13. What are fundamental types in JavaScript?

JavaScript contains 9 fundamental data types:

Number

The Number data type represents numbers in JavaScript. It can be used for both integers and floating-point numbers. The value NaN is also considered of the Number type.

let age = 20;
console.info(typeof age) // number

String

The String data type represents sequences of text characters. Text is enclosed in single or double quotes.

let name = "Bob";
console.info(typeof name) // string

Boolean

The Boolean data type can have one of two values: true (truth) or false (falsehood). It is used to represent logical states.

let isMale = true;
console.info(typeof isMale) // boolean

Null

The Null data type represents the absence of a value or emptiness. It is a special value that signifies a lack of data.

Pay attention to typeof result!

let data = null;
console.info(typeof data) // object

Undefined

The Undefined data type represents a variable that has been declared but hasn't been assigned a value. It's also the default value of variables.

let data;
console.info(data); // undefined
console.info(typeof data) // undefined

Object

The Object data type represents complex objects that can contain various properties and methods. Objects are fundamental data structures in JavaScript.

let person = {
  name: "Bob",
  age: 20,
};
console.info(typeof person) // object

Function

The Function data type represents functions in JavaScript. Functions are blocks of code that can be called and used to perform specific actions.

function add(a, b) {
  return a + b;
}
console.info(typeof add) // function

Symbol (from ES6)

The Symbol data type was introduced in ECMAScript 6 (ES6). It's a unique and immutable type used to create unique property keys in objects.

const mySymbol1 = Symbol("symbol");
const mySymbol2 = Symbol("symbol");
const obj = {};
obj[mySymbol1] = "abc";
obj[mySymbol2] = "cba";
console.info(obj[mySymbol1]) // abc
console.info(obj[mySymbol2]) // cba
console.info(typeof mySymbol1) // symbol

BigInt (from ES11)

The BigInt data type was introduced in ECMAScript 11 (ES11). It's a special data type used to represent arbitrarily large numbers with no numerical limits. It's denoted by adding n or N at the end of a number.

const bigNumber = 1234567890123456789012345678901234567890n;
console.info(typeof mySymbol1) // bigint