lodash/test/isNil.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { falsey, args, slice, symbol, realm } from './utils';
import isNil from '../src/isNil';

describe('isNil', () => {
    it('should return `true` for nullish values', () => {
        assert.strictEqual(isNil(null), true);
        assert.strictEqual(isNil(), true);
        assert.strictEqual(isNil(undefined), true);
    });

    it('should return `false` for non-nullish values', () => {
        const expected = lodashStable.map(falsey, (value) => value === null);

        const actual = lodashStable.map(falsey, (value, index) => (index ? isNil(value) : isNil()));

        assert.deepStrictEqual(actual, expected);

        assert.strictEqual(isNil(args), false);
        assert.strictEqual(isNil([1, 2, 3]), false);
        assert.strictEqual(isNil(true), false);
        assert.strictEqual(isNil(new Date()), false);
        assert.strictEqual(isNil(new Error()), false);
        assert.strictEqual(isNil(slice), false);
        assert.strictEqual(isNil({ a: 1 }), false);
        assert.strictEqual(isNil(1), false);
        assert.strictEqual(isNil(/x/), false);
        assert.strictEqual(isNil('a'), false);

        if (Symbol) {
            assert.strictEqual(isNil(symbol), false);
        }
    });

    it('should work with nils from another realm', () => {
        if (realm.object) {
            assert.strictEqual(isNil(realm.null), true);
            assert.strictEqual(isNil(realm.undefined), true);
        }
    });
});