lodash/test/head.spec.ts

import assert from 'node:assert';
import lodashStable from 'lodash';
import { arrayProto, LARGE_ARRAY_SIZE } from './utils';
import head from '../src/head';
import first from '../src/first';

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

    it('should return the first element', () => {
        assert.strictEqual(head(array), 1);
    });

    it('should return `undefined` when querying empty arrays', () => {
        arrayProto[0] = 1;
        assert.strictEqual(head([]), undefined);
        arrayProto.length = 0;
    });

    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, head);

        assert.deepStrictEqual(actual, [1, 4, 7]);
    });

    it('should be aliased', () => {
        assert.strictEqual(first, head);
    });

    it('should return an unwrapped value when implicitly chaining', () => {
        const wrapped = _(array);
        assert.strictEqual(wrapped.head(), 1);
        assert.strictEqual(wrapped.first(), 1);
    });

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

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

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

        lodashStable.each(['head', 'first'], (methodName) => {
            lodashStable.times(2, (index) => {
                const array = index ? largeArray : smallArray,
                    actual = _(array).filter(isEven)[methodName]();

                assert.strictEqual(actual, _[methodName](_.filter(array, isEven)));
            });
        });
    });
});