lodash/test/last.spec.ts

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

describe('last', () => {
    const array = [1, 2, 3, 4];

    it('should return the last element', () => {
        assert.strictEqual(last(array), 4);
    });

    it('should return `undefined` when querying empty arrays', () => {
        const array = [];
        array['-1'] = 1;

        assert.strictEqual(last([]), undefined);
    });

    it('should work as an iteratee for methods like `_.map`', () => {
        const array = [
                [1, 2, 3],
                [4, 5, 6],
                [7, 8, 9],
            ],
            actual = lodashStable.map(array, last);

        assert.deepStrictEqual(actual, [3, 6, 9]);
    });

    it('should return an unwrapped value when implicitly chaining', () => {
        assert.strictEqual(_(array).last(), 4);
    });

    it('should return a wrapped value when explicitly chaining', () => {
        assert.ok(_(array).chain().last() instanceof _);
    });

    it('should not execute immediately when explicitly chaining', () => {
        const wrapped = _(array).chain().last();
        assert.strictEqual(wrapped.__wrapped__, array);
    });

    it('should work in a lazy sequence', () => {
        const largeArray = lodashStable.range(LARGE_ARRAY_SIZE),
            smallArray = array;

        lodashStable.times(2, (index) => {
            const array = index ? largeArray : smallArray,
                wrapped = _(array).filter(isEven);

            assert.strictEqual(wrapped.last(), last(_.filter(array, isEven)));
        });
    });
});