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)

Types

| 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" | | 2n^63n | BigInt | "BigInt" | | [-]Infinity | Infinity | "Infinity" | | NaN | NaN | "NaN" | | Math | Math | "Math" | | Symbol("*") | Symbol | "Symbol" | | /.*/g/new RegExp(".*") | RegExp | "RegExp" | | new Error("message") | Error | "Error" | | new EvalError("message") | EvalError | "EvalError" | | new RangeError("message") | RangeError | "RangeError" | | new ReferenceError("message") | ReferenceError | "ReferenceError" | | new SyntaxError("message") | SyntaxError | "SyntaxError" | | new TypeError("message") | TypeError | "TypeError" | | new URIError("message") | URIError | "URIError" | | new AggregateError("message") | AggregateError | "AggregateError" | | new Intl.Segmenter() | Segmenter | "Segmenter" | | new Date() | Date | "Date" | | new URL("https://github.com") | URL | "URL" | | fs.createReadStream(buffer) | ReadStream | "ReadStream" | | fs.createWriteStream("/dev/null") | WriteStream | "WriteStream" | | const buffer = Buffer.from("data") | Buffer | "Buffer" | | new ArrayBuffer(1024) | ArrayBuffer | "ArrayBuffer" | | new Int8Array([-128, 127]) | [Int8Array] | "Int8Array" | |new Uint8Array([0, 255]) | [Uint8Array] | "Uint8Array" | |new new Uint8ClampedArray([0, 255]) | [Uint8ClampedArray] | "Uint8ClampedArray" | |new Int16Array([-32768, 32767]) | [Int16Array] | "Int16Array" | |new Uint16Array([0, 65535]) | [Uint16Array] | "Uint16Array" | |new Int32Array([-2147483648, 2147483647]) | [Int32Array] | "Int32Array" | |new Uint32Array([0, 4294967295]) | [Uint32Array] | "Uint32Array" | |new Float32Array([-3.4e38, 3.4e38]) | [Float32Array] | "Float32Array" | |new Float64Array([-1.8e308, 1.8e308]) | [Float64Array] | "Float64Array" | |new BigInt64Array([-2n^63n, 2n^63n]) | [BigInt64Array] | "BigInt64Array" | |new BigUint64Array([0n, 2n^63n]) | [BigUint64Array] | "BigUint64Array" | |[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"][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