The 10-Day JavaScript Challenge - Day 7: Factorial Number

factorialNumber.js

// basic with for loop
const factorialNumber = num => {
    let result = 1;

    for(let i = result + 1; i <= num; i++) {
        result *= i;
    }

    return result;
};

// refactored w/ higher order functions
const factorialNumber = num => [...Array(num).keys()]
    .map(n => n + 1)
    .reduce((a, c) => a * c, 1);


describe('factorialNumber()', () => {
    it('returns factorial of number param', () => {
        // arrange
        const num = 5;
        
        // act
        const result = factorialNumber(num);

        // log
        console.log("result: ", result);
        
        // assert
        expect(result).toBe(120);
    });
});