lodash/test/flatten-methods.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { args, _ } from './utils';
import flatten from '../src/flatten';
import flattenDeep from '../src/flattenDeep';
import flattenDepth from '../src/flattenDepth';

describe('flatten methods', () => {
    const array = [1, [2, [3, [4]], 5]],
        methodNames = ['flatten', 'flattenDeep', 'flattenDepth'];

    it('should flatten `arguments` objects', () => {
        const array = [args, [args]];

        assert.deepStrictEqual(flatten(array), [1, 2, 3, args]);
        assert.deepStrictEqual(flattenDeep(array), [1, 2, 3, 1, 2, 3]);
        assert.deepStrictEqual(flattenDepth(array, 2), [1, 2, 3, 1, 2, 3]);
    });

    it('should treat sparse arrays as dense', () => {
        const array = [[1, 2, 3], Array(3)],
            expected = [1, 2, 3];

        expected.push(undefined, undefined, undefined);

        lodashStable.each(methodNames, (methodName) => {
            const actual = _[methodName](array);
            assert.deepStrictEqual(actual, expected);
            assert.ok('4' in actual);
        });
    });

    it('should flatten objects with a truthy `Symbol.isConcatSpreadable` value', () => {
        if (Symbol && Symbol.isConcatSpreadable) {
            const object = { '0': 'a', length: 1 },
                array = [object],
                expected = lodashStable.map(methodNames, lodashStable.constant(['a']));

            object[Symbol.isConcatSpreadable] = true;

            const actual = lodashStable.map(methodNames, (methodName) => _[methodName](array));

            assert.deepStrictEqual(actual, expected);
        }
    });

    it('should work with extremely large arrays', () => {
        lodashStable.times(3, (index) => {
            const expected = Array(5e5);
            try {
                let func = flatten;
                if (index === 1) {
                    func = flattenDeep;
                } else if (index === 2) {
                    func = flattenDepth;
                }
                assert.deepStrictEqual(func([expected]), expected);
            } catch (e) {
                assert.ok(false, e.message);
            }
        });
    });

    it('should work with empty arrays', () => {
        const array = [[], [[]], [[], [[[]]]]];

        assert.deepStrictEqual(flatten(array), [[], [], [[[]]]]);
        assert.deepStrictEqual(flattenDeep(array), []);
        assert.deepStrictEqual(flattenDepth(array, 2), [[[]]]);
    });

    it('should support flattening of nested arrays', () => {
        assert.deepStrictEqual(flatten(array), [1, 2, [3, [4]], 5]);
        assert.deepStrictEqual(flattenDeep(array), [1, 2, 3, 4, 5]);
        assert.deepStrictEqual(flattenDepth(array, 2), [1, 2, 3, [4], 5]);
    });

    it('should return an empty array for non array-like objects', () => {
        const expected = [],
            nonArray = { '0': 'a' };

        assert.deepStrictEqual(flatten(nonArray), expected);
        assert.deepStrictEqual(flattenDeep(nonArray), expected);
        assert.deepStrictEqual(flattenDepth(nonArray, 2), expected);
    });

    it('should return a wrapped value when chaining', () => {
        let wrapped = _(array),
            actual = wrapped.flatten();

        assert.ok(actual instanceof _);
        assert.deepEqual(actual.value(), [1, 2, [3, [4]], 5]);

        actual = wrapped.flattenDeep();

        assert.ok(actual instanceof _);
        assert.deepEqual(actual.value(), [1, 2, 3, 4, 5]);

        actual = wrapped.flattenDepth(2);

        assert.ok(actual instanceof _);
        assert.deepEqual(actual.value(), [1, 2, 3, [4], 5]);
    });
});