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    which-boxed-primitive

    1.0.2 • Public • Published

    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

    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

    Install

    npm i which-boxed-primitive

    DownloadsWeekly Downloads

    10,933,606

    Version

    1.0.2

    License

    MIT

    Unpacked Size

    15 kB

    Total Files

    11

    Last publish

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