which-builtin-type

What is the type of this builtin JavaScript value? Works cross-realm, without instanceof, and can not be fooled by a constructor property.

Example

1var whichBuiltinType = require('which-builtin-type');
2var assert = require('assert');
3
4assert.equal(undefined, whichBuiltinType(undefined));
5assert.equal(null, whichBuiltinType(null));
6assert.equal('Boolean', whichBuiltinType(false));
7assert.equal('Boolean', whichBuiltinType(true));
8assert.equal('Array', whichBuiltinType([]));
9assert.equal('Object', whichBuiltinType({}));
10assert.equal('RegExp', whichBuiltinType(/a/g));
11assert.equal('RegExp', whichBuiltinType(new RegExp('a', 'g')));
12assert.equal('Date', whichBuiltinType(new Date()));
13assert.equal('Number', whichBuiltinType(42));
14assert.equal('Number', whichBuiltinType(NaN));
15assert.equal('Number', whichBuiltinType(Infinity));
16assert.equal('Number', whichBuiltinType(new Number(42)));
17assert.equal('String', whichBuiltinType('foo'));
18assert.equal('String', whichBuiltinType(Object('foo')));
19assert.equal('Function', whichBuiltinType(function () {}));
20assert.equal('GeneratorFunction', whichBuiltinType(function* () {}));
21assert.equal('Function', whichBuiltinType(x => x * x));
22assert.equal('Array', whichBuiltinType([]));
23assert.equal('Int8Array', whichBuiltinType(new Int8Array()));
24assert.equal('Uint8Array', whichBuiltinType(new Uint8Array()));
25assert.equal('Uint8ClampedArray', whichBuiltinType(new Uint8ClampedArray()));
26assert.equal('Int16Array', whichBuiltinType(new Int16Array()));
27assert.equal('Uint16Array', whichBuiltinType(new Uint16Array()));
28assert.equal('Int32Array', whichBuiltinType(new Int32Array()));
29assert.equal('Uint32Array', whichBuiltinType(new Uint32Array()));
30assert.equal('Float32Array', whichBuiltinType(new Float32Array()));
31assert.equal('Float64Array', whichBuiltinType(new Float64Array()));
32assert.equal('BigInt64Array', whichBuiltinType(new BigInt64Array()));
33assert.equal('BigUint64Array', whichBuiltinType(new BigUint64Array()));

Tests

Simply clone the repo, npm install, and run npm test