74 lines
3 KiB
Markdown
74 lines
3 KiB
Markdown
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# which-boxed-primitive <sup>[![Version Badge][2]][1]</sup>
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[![dependency status][5]][6]
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[![dev dependency status][7]][8]
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[![License][license-image]][license-url]
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[![Downloads][downloads-image]][downloads-url]
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[![npm badge][11]][1]
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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.
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## Example
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```js
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var whichBoxedPrimitive = require('which-boxed-primitive');
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var assert = require('assert');
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// unboxed primitives return `null`
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// boxed primitives return the builtin constructor name
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assert.equal(whichBoxedPrimitive(undefined), null);
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assert.equal(whichBoxedPrimitive(null), null);
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assert.equal(whichBoxedPrimitive(false), null);
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assert.equal(whichBoxedPrimitive(true), null);
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assert.equal(whichBoxedPrimitive(new Boolean(false)), 'Boolean');
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assert.equal(whichBoxedPrimitive(new Boolean(true)), 'Boolean');
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assert.equal(whichBoxedPrimitive(42), null);
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assert.equal(whichBoxedPrimitive(NaN), null);
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assert.equal(whichBoxedPrimitive(Infinity), null);
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assert.equal(whichBoxedPrimitive(new Number(42)), 'Number');
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assert.equal(whichBoxedPrimitive(new Number(NaN)), 'Number');
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assert.equal(whichBoxedPrimitive(new Number(Infinity)), 'Number');
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assert.equal(whichBoxedPrimitive(''), null);
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assert.equal(whichBoxedPrimitive('foo'), null);
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assert.equal(whichBoxedPrimitive(new String('')), 'String');
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assert.equal(whichBoxedPrimitive(new String('foo')), 'String');
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assert.equal(whichBoxedPrimitive(Symbol()), null);
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assert.equal(whichBoxedPrimitive(Object(Symbol()), 'Symbol');
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assert.equal(whichBoxedPrimitive(42n), null);
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assert.equal(whichBoxedPrimitive(Object(42n), 'BigInt');
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// non-boxed-primitive objects return `undefined`
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assert.equal(whichBoxedPrimitive([]), undefined);
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assert.equal(whichBoxedPrimitive({}), undefined);
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assert.equal(whichBoxedPrimitive(/a/g), undefined);
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assert.equal(whichBoxedPrimitive(new RegExp('a', 'g')), undefined);
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assert.equal(whichBoxedPrimitive(new Date()), undefined);
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assert.equal(whichBoxedPrimitive(function () {}), undefined);
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assert.equal(whichBoxedPrimitive(function* () {}), undefined);
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assert.equal(whichBoxedPrimitive(x => x * x), undefined);
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assert.equal(whichBoxedPrimitive([]), undefined);
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```
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## Tests
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Simply clone the repo, `npm install`, and run `npm test`
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[1]: https://npmjs.org/package/which-boxed-primitive
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[2]: https://versionbadg.es/inspect-js/which-boxed-primitive.svg
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[5]: https://david-dm.org/inspect-js/which-boxed-primitive.svg
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[6]: https://david-dm.org/inspect-js/which-boxed-primitive
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[7]: https://david-dm.org/inspect-js/which-boxed-primitive/dev-status.svg
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[8]: https://david-dm.org/inspect-js/which-boxed-primitive#info=devDependencies
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[11]: https://nodei.co/npm/which-boxed-primitive.png?downloads=true&stars=true
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[license-image]: https://img.shields.io/npm/l/which-boxed-primitive.svg
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[license-url]: LICENSE
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[downloads-image]: https://img.shields.io/npm/dm/which-boxed-primitive.svg
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[downloads-url]: https://npm-stat.com/charts.html?package=which-boxed-primitive
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