README
Accurately determine native type of values
Usage
Standard values
const typeOf = require('native-type-of');
// Primitives
typeOf('abc') === 'string';
typeOf(123) === 'number';
typeOf(true) === 'boolean';
typeOf(Symbol()) === 'symbol';
typeOf(100n) === 'bigint';
typeOf(null) === 'null';
typeOf(undefined) === 'undefined';
// Functions
typeOf(function() {}) === 'Function';
typeOf(() => {}) === 'Function';
typeOf(async function() {}) === 'Function';
typeOf(function*() {}) === 'Function';
typeOf(async function*() {}) === 'Function';
// Objects
typeOf({}) === 'Object';
class C {}
typeOf(new C()) === 'Object';
// Built-ins
typeOf([]) === 'Array';
typeOf(/^abc$/) === 'RegExp';
typeOf(new Date()) === 'Date';
typeOf(Promise.resolve()) === 'Promise';
typeOf(new Set()) === 'Set';
typeOf(new Map()) === 'Map';
typeOf(new WeakSet()) === 'WeakSet';
typeOf(new WeakMap()) === 'WeakMap';
typeOf(new WeakRef({})) === 'WeakRef';
typeOf(new FinalizationRegistry(() => {})) === 'FinalizationRegistry';
// Boxed primitives
typeOf(new String('')) === 'String';
typeOf(new Number(123)) === 'Number';
typeOf(new Boolean(true)) === 'Boolean';
typeOf(Object(BigInt(100)) === 'BigInt';
typeOf(Object(Symbol()) === 'Symbol';
// Errors
typeOf(new Error()) === 'Error';
typeOf(new TypeError()) === 'TypeError';
typeOf(new ReferenceError()) === 'ReferenceError';
// ...etc
// Buffers
typeOf(new ArrayBuffer(8)) === 'ArrayBuffer';
typeOf(new SharedArrayBuffer(8)) === 'SharedArrayBuffer';
typeOf(new Uint8Array([1, 2, 3])) === 'Uint8Array';
typeOf(new Int32Array([1, 2, 3])) === 'Int32Array';
// ...etc
Values with altered prototype
If the prototype chain is altered, this package aims to return the native type of the underlying object.
This is where this package differs from others like kind-of.
const map = new Map();
Object.setPrototypeOf(map, Array.prototype);
typeOf(map) === 'Map';
It also ignores custom [Symbol.toStringTag]
properties.
const obj = { [Symbol.toStringTag]: 'Gizmo' };
typeOf(obj) === 'Object';
Known issues
There are a few rare cases where native type cannot be correctly determined:
typeOf( Object.setPrototypeOf( Promise.resolve(), Array.prototype ) ) === 'Object'
(issue)typeOf( Object.setPrototypeOf( new Error(), Map.prototype ) ) === 'Object'
(issue)typeOf( Object.setPrototypeOf( {}, TypeError.prototype ) ) === 'TypeError'
(issue)
These are the only known cases where the result is inaccurate.
Versioning
This module follows semver. Breaking changes will only be made in major version updates.
All active NodeJS release lines are supported (v12+ at time of writing). After a release line of NodeJS reaches end of life according to Node's LTS schedule, support for that version of Node may be dropped at any time, and this will not be considered a breaking change. Dropping support for a Node version will be made in a minor version update (e.g. 1.2.0 to 1.3.0). If you are using a Node version which is approaching end of life, pin your dependency of this module to patch updates only using tilde (~
) e.g. ~1.2.3
to avoid breakages.
Tests
Use npm test
to run the tests. Use npm run cover
to check coverage.
Changelog
See changelog.md
Issues
If you discover a bug, please raise an issue on Github. https://github.com/overlookmotel/native-type-of/issues
Contribution
Pull requests are very welcome. Please:
- ensure all tests pass before submitting PR
- add tests for new features
- document new functionality/API additions in README
- do not add an entry to Changelog (Changelog is created when cutting releases)