Reliable Type

Reliable runtime type information.

Install

pnpm install reliable-type

Example

The provided type method is more reliable than some combination of typeof and instanceof. While the .constructor Object property is strong —and recommended, in absence of a dependency like this—it can technically be reassigned. It will always return the correct type as an informative, specific Type or tag String. Extra types are also available to import:

import assert from "node:assert/strict"
import { type, types, tag, tags } from "reliable-type"
import { GeneratorFunction } from "reliable-type/types"

function* generator() { yield * [1, 2, 3] }

const Type = type(generator)
const Tag  =  tag(generator)

assert.equal(Type, GeneratorFunction)
assert.equal(Tag, "GeneratorFunction")

assert.equal(Type, types.GeneratorFunction)
assert.equal(Tag,   tags.GeneratorFunction)

Expression	type	tag
undefined	undefined	"undefined"
null	null	"null"
true/false	Boolean	"Boolean"
"string"	String	"String"
-0/1_000/0.1	Number	"Number"
0xAf/0o1/0b1	Number	"Number"
3.1415e+1/Math.PI	Number	"Number"
1_000_000n	BigInt	"BigInt"
[-]Infinity	Infinity	"Infinity"
NaN	NaN	"NaN"
Math	Math	"Math"
Symbol("*")	Symbol	"Symbol"
new Intl.Segmenter()	Segmenter	"Segmenter"
new Date()	Date	"Date"
/.*/g/new RegExp(".*")	RegExp	"RegExp"
new URL("https://github.com")	URL	"URL"
const buffer = Buffer.from("data")	Buffer	"Buffer"
fs.createReadStream(buffer)	ReadStream	"ReadStream"
fs.createWriteStream("/dev/null")	WriteStream	"WriteStream"
new Uint8Array([0, 255])	Uint8Array	"Uint8Array"
[1 ,2 ,3]/Array.from("abc")	Array	"Array"
new Set([1, 2, 3])	Set	"Set"
new WeakSet()	WeakSet	"WeakSet"
new WeakMap()	WeakMap	"WeakMap"
const map = new Map().set("a", 1)	Map	"Map"
map.entries()	Iterator	"Iterator"
const object = { a: 1, b: 2 }	Object	"Object"
new Proxy(object, {})	Proxy	"Proxy"
Proxy.revocable(object, {})	Proxy	"Proxy"
{ [Symbol.toStringTag]: "tag" }	"tag"	"tag"
JSON	JSON	"JSON"
function() { return arguments }(1, 2)	Arguments	"Arguments"
[].reduce/() => {}	Function	"Function"
async () => Promise.resolve(true)	AsyncFunction	"AsyncFunction"
Promise.resolve(true)	Promise	"Promise"
function* generator() { yield * [1, 2] }	GeneratorFunction	"GeneratorFunction"
generator()	Generator	"Generator"
async function* gen() { yield * [1, 2] }	AsyncGeneratorFunction	"AsyncGeneratorFunction"
gen()	AsyncGenerator	"AsyncGenerator"
new (class Class {})()	Class	"Class"
new (class Extended extends Class {})()	ExtendedClass	"ExtendedClass"
fs.opendir(dir)	Dir	"Dir"
fs.readdir(dir, { withFileTypes: true })	Dirent	"Dirent"

Aliases

import { typeOf, toStringTag } from "reliable-type"

License

MIT © Daniel Bayley