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