⚖️callable vs. constructable

JS ⟩ value ⟩ object ⟩ create ⟩ new ⟩ callable vs. constructable

if a function can be invoked in the form F(), it's callable.
if a function can be invoked in the form new F(), it's constructable.

not every function is callable, for example, Map is a function, but calling it with Map() throws a TypeError❗

not every function is constructable, for example, Symbol is a function, but calling it with new Symbol() throws a TypeError❗

replit ⟩ callable vs. constructable

// Array is callable & constructable, same effect.
let arr1 = Array(3);
let arr2 = new Array(3);

let map = Map();            // Map is not callable.
//        ^^^
// ⛔ TypeError: Constructor `Map` requires 'new'

let sym = new Symbol();     // Symbol is not constructable.
//        ^^^
// ⛔ TypeError: `Symbol` is not a constructor

arr1,    // [ , , ] (3 empthy items)
arr2,    // [ , , ] (3 empthy items)

Map instanceof Function,    // true
Symbol instanceof Function, // true

function

F()

new F()

note

Array, Error, Function

✅

same effect

Boolean, String, Number

primitive

wrapper object

Date

string

object

Symbol, BigInt

✅

⛔️ TypeError

Proxy, Map

⛔️ TypeError

✅

class

⛔️ TypeError

✅

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Last updated 3 years ago

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