lodash/test/slice.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { falsey, LARGE_ARRAY_SIZE } from './utils';
import slice from '../src/slice';

describe('slice', () => {
    const array = [1, 2, 3];

    it('should use a default `start` of `0` and a default `end` of `length`', () => {
        const actual = slice(array);
        assert.deepStrictEqual(actual, array);
        assert.notStrictEqual(actual, array);
    });

    it('should work with a positive `start`', () => {
        assert.deepStrictEqual(slice(array, 1), [2, 3]);
        assert.deepStrictEqual(slice(array, 1, 3), [2, 3]);
    });

    it('should work with a `start` >= `length`', () => {
        lodashStable.each([3, 4, 2 ** 32, Infinity], (start) => {
            assert.deepStrictEqual(slice(array, start), []);
        });
    });

    it('should treat falsey `start` values as `0`', () => {
        const expected = lodashStable.map(falsey, lodashStable.constant(array));

        const actual = lodashStable.map(falsey, (start) => slice(array, start));

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

    it('should work with a negative `start`', () => {
        assert.deepStrictEqual(slice(array, -1), [3]);
    });

    it('should work with a negative `start` <= negative `length`', () => {
        lodashStable.each([-3, -4, -Infinity], (start) => {
            assert.deepStrictEqual(slice(array, start), array);
        });
    });

    it('should work with `start` >= `end`', () => {
        lodashStable.each([2, 3], (start) => {
            assert.deepStrictEqual(slice(array, start, 2), []);
        });
    });

    it('should work with a positive `end`', () => {
        assert.deepStrictEqual(slice(array, 0, 1), [1]);
    });

    it('should work with a `end` >= `length`', () => {
        lodashStable.each([3, 4, 2 ** 32, Infinity], (end) => {
            assert.deepStrictEqual(slice(array, 0, end), array);
        });
    });

    it('should treat falsey `end` values, except `undefined`, as `0`', () => {
        const expected = lodashStable.map(falsey, (value) => (value === undefined ? array : []));

        const actual = lodashStable.map(falsey, (end, index) =>
            index ? slice(array, 0, end) : slice(array, 0),
        );

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

    it('should work with a negative `end`', () => {
        assert.deepStrictEqual(slice(array, 0, -1), [1, 2]);
    });

    it('should work with a negative `end` <= negative `length`', () => {
        lodashStable.each([-3, -4, -Infinity], (end) => {
            assert.deepStrictEqual(slice(array, 0, end), []);
        });
    });

    it('should coerce `start` and `end` to integers', () => {
        const positions = [[0.1, 1.6], ['0', 1], [0, '1'], ['1'], [NaN, 1], [1, NaN]];

        const actual = lodashStable.map(positions, (pos) => slice.apply(_, [array].concat(pos)));

        assert.deepStrictEqual(actual, [[1], [1], [1], [2, 3], [1], []]);
    });

    it('should work as an iteratee for methods like `_.map`', () => {
        const array = [[1], [2, 3]],
            actual = lodashStable.map(array, slice);

        assert.deepStrictEqual(actual, array);
        assert.notStrictEqual(actual, array);
    });

    it('should work in a lazy sequence', () => {
        const array = lodashStable.range(1, LARGE_ARRAY_SIZE + 1),
            length = array.length,
            wrapped = _(array);

        lodashStable.each(['map', 'filter'], (methodName) => {
            assert.deepEqual(wrapped[methodName]().slice(0, -1).value(), array.slice(0, -1));
            assert.deepEqual(wrapped[methodName]().slice(1).value(), array.slice(1));
            assert.deepEqual(wrapped[methodName]().slice(1, 3).value(), array.slice(1, 3));
            assert.deepEqual(wrapped[methodName]().slice(-1).value(), array.slice(-1));

            assert.deepEqual(wrapped[methodName]().slice(length).value(), array.slice(length));
            assert.deepEqual(wrapped[methodName]().slice(3, 2).value(), array.slice(3, 2));
            assert.deepEqual(
                wrapped[methodName]().slice(0, -length).value(),
                array.slice(0, -length),
            );
            assert.deepEqual(wrapped[methodName]().slice(0, null).value(), array.slice(0, null));

            assert.deepEqual(
                wrapped[methodName]().slice(0, length).value(),
                array.slice(0, length),
            );
            assert.deepEqual(wrapped[methodName]().slice(-length).value(), array.slice(-length));
            assert.deepEqual(wrapped[methodName]().slice(null).value(), array.slice(null));

            assert.deepEqual(wrapped[methodName]().slice(0, 1).value(), array.slice(0, 1));
            assert.deepEqual(wrapped[methodName]().slice(NaN, '1').value(), array.slice(NaN, '1'));

            assert.deepEqual(wrapped[methodName]().slice(0.1, 1.1).value(), array.slice(0.1, 1.1));
            assert.deepEqual(wrapped[methodName]().slice('0', 1).value(), array.slice('0', 1));
            assert.deepEqual(wrapped[methodName]().slice(0, '1').value(), array.slice(0, '1'));
            assert.deepEqual(wrapped[methodName]().slice('1').value(), array.slice('1'));
            assert.deepEqual(wrapped[methodName]().slice(NaN, 1).value(), array.slice(NaN, 1));
            assert.deepEqual(wrapped[methodName]().slice(1, NaN).value(), array.slice(1, NaN));
        });
    });
});