which-boxed-primitive Version Badge

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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

```js 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