which-boxed-primitive (1.1.1)

2026-02-24T14:08:35Z

Setup this registry in your project .npmrc file:

registry=

To install the package using npm, run the following command:

npm install which-boxed-primitive@1.1.1

or add it to the package.json file:

"which-boxed-primitive": "1.1.1"

For more information on the npm registry, see the documentation.

which-boxed-primitive

Which kind of boxed JS primitive is this? This module works cross-realm/iframe, does not depend on instanceof or mutable properties, and works despite ES6 Symbol.toStringTag.

Example

var whichBoxedPrimitive = require('which-boxed-primitive');
var assert = require('assert');

// unboxed primitives return `null`
// boxed primitives return the builtin constructor name

assert.equal(whichBoxedPrimitive(undefined), null);
assert.equal(whichBoxedPrimitive(null), null);

assert.equal(whichBoxedPrimitive(false), null);
assert.equal(whichBoxedPrimitive(true), null);
assert.equal(whichBoxedPrimitive(new Boolean(false)), 'Boolean');
assert.equal(whichBoxedPrimitive(new Boolean(true)), 'Boolean');

assert.equal(whichBoxedPrimitive(42), null);
assert.equal(whichBoxedPrimitive(NaN), null);
assert.equal(whichBoxedPrimitive(Infinity), null);
assert.equal(whichBoxedPrimitive(new Number(42)), 'Number');
assert.equal(whichBoxedPrimitive(new Number(NaN)), 'Number');
assert.equal(whichBoxedPrimitive(new Number(Infinity)), 'Number');

assert.equal(whichBoxedPrimitive(''), null);
assert.equal(whichBoxedPrimitive('foo'), null);
assert.equal(whichBoxedPrimitive(new String('')), 'String');
assert.equal(whichBoxedPrimitive(new String('foo')), 'String');

assert.equal(whichBoxedPrimitive(Symbol()), null);
assert.equal(whichBoxedPrimitive(Object(Symbol()), 'Symbol');

assert.equal(whichBoxedPrimitive(42n), null);
assert.equal(whichBoxedPrimitive(Object(42n), 'BigInt');

// non-boxed-primitive objects return `undefined`
assert.equal(whichBoxedPrimitive([]), undefined);
assert.equal(whichBoxedPrimitive({}), undefined);
assert.equal(whichBoxedPrimitive(/a/g), undefined);
assert.equal(whichBoxedPrimitive(new RegExp('a', 'g')), undefined);
assert.equal(whichBoxedPrimitive(new Date()), undefined);
assert.equal(whichBoxedPrimitive(function () {}), undefined);
assert.equal(whichBoxedPrimitive(function* () {}), undefined);
assert.equal(whichBoxedPrimitive(x => x * x), undefined);
assert.equal(whichBoxedPrimitive([]), undefined);

Tests

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

Dependencies

ID	Version
is-bigint	^1.1.0
is-boolean-object	^1.2.1
is-number-object	^1.1.1
is-string	^1.1.1
is-symbol	^1.1.1

Development Dependencies

ID	Version
@arethetypeswrong/cli	^0.17.1
@ljharb/eslint-config	^21.1.1
@ljharb/tsconfig	^0.2.2
@types/for-each	^0.3.3
@types/object-inspect	^1.13.0
@types/tape	^5.7.0
auto-changelog	^2.5.0
encoding	^0.1.13
es-value-fixtures	^1.5.0
eslint	=8.8.0
for-each	^0.3.3
in-publish	^2.0.1
npmignore	^0.3.1
nyc	^10.3.2
object-inspect	^1.13.3
safe-publish-latest	^2.0.0
tape	^5.9.0
typescript	next

boxed primitive object ecmascript javascript which

Details

npm

2026-02-24 14:08:35 +00:00

0

Jordan Harband

Project Site

MIT

latest

6.6 KiB

Assets (1)

which-boxed-primitive-1.1.1.tgz 6.6 KiB

Versions (1) View all

1.1.1

2026-02-24

which-boxed-primitive (1.1.1)

Installation

About this package

which-boxed-primitive

Example

Tests

Dependencies

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