@everget/typeof

typeOf

A smart replacement of the typeof operator and robust type checker. This is my first ever published module on npm (2017). I have rewritten it to the modern stack (TypeScript, Vitest) without functional changes.

Installation

pnpm add @everget/typeof

Usage

const typeOf = require('@everget/typeof');
// or
import typeOf from '@everget/typeof';

let value = 'awesome string';

typeOf(value)();
// => 'string'

typeOf(value) == 'string';
// => true

typeOf(value).expect('string');
// => true

typeOf(value).expect('number');
// => TypeError: The value is of type `string`, but expected `number`

/** NOTE: you must use `==` operator for correct work */
let isMap = (value) => typeOf(value)() == 'map';

let smth = new Map();

if (isMap(smth)) {
  /** Do your staff */
}

let isFunction = (value) => {
  return typeOf(value).expect('function|asyncfunction|generatorfunction');
}

let smth = async () => {};

if (isFunction(smth)) {
  /** Do your staff */
}

function sum(a, b) {
  typeOf(a).expect('number');
  typeOf(b).expect('number');

  return typeOf(a + b).expect('number') && (a + b);
}

sum(1, () => {});
// => TypeError: The value is of type `function`, but expected `number`

sum(1, 2);
// => 3

Examples of returned values

ES

Value	Type
{}	'object'
Math	'math'
JSON	'object'
function() {}	'function'
[]	'array'
null	'null'
(function() { return arguments })()	'arguments'
new Error	'error'
undefined	'underfined'

ES6, ES7

Value	Type
Reflect	'object'
class {}	'function'
Proxy	'function'
new Proxy({}, {})	'object'
() => {}	'function'
function* () {}	'generatorfunction'
async function() {}	'asyncfunction'
Symbol	'function'
Symbol()	'symbol'
new Map	'map'
new WeakMap	'weakmap'
new Set	'set'
new WeakSet	'weakset'
[1, 2, 3].entries()	'arrayiterator'
new Set().entries()	'setiterator'
new Map().entries()	'mapiterator'
''Symbol.iterator	'stringiterator'
new ArrayBuffer()	'arraybuffer'
new DataView(new ArrayBuffer)	'dataview'

Browser

Value	Type
window	'global'
document	'htmldocument'
localStorage	'storage'
new DOMException	'domexception'
document.createDocumentFragment()	'documentfragment'
document.createElement('a')	'htmlanchorelement'
document.createElement('body')	'htmlbodyelement'
document.createElement('template')	'htmltemplateelement'
document.createTextNode('')	'text'
document.createComment('')	'comment'

Node.js

Value	Type
global	'global'
process	'process'

Tests

npm test

Release History

• 0.1.0 Initial release
• 0.1.1 Added detection of typed arrays
• 2.0.0 Corrections for global object, Math, JSON, async functions and generators
• 3.0.0 Implemented new usage syntax. Added correct detection of iterators