Best practice of creating object from reduce

Question

I wrote an algorithm using reduce which creates an object with two other objects inside, however I found unreadable.

In search of inspiration to refactor the algorithm I ended up searching in codegrepper and google, but I did not get.

I believe that the algorithm is relatively easy and used within systems, if anyone makes a suggestion I will be grateful.

Follow code I wrote firsthand:

let isbns = [
    '64646464',
    '978-8575228050',
    '978-8573076103',
    '6586057043'
]
let links = ['Nenhum resultado para 64646464.',
    '/Problemas-Cl%C3%A1ssicos-Ci%C3%AAncia-Computa%C3%A7%C3%A3o-Python/dp/8575228056',
    '/Padr%C3%B5es-Projetos-Solu%C3%A7%C3%B5es-Reutiliz%C3%A1veis-Orientados/dp/8573076100',
    '/Migrando-Sistemas-Monol%C3%ADticos-Para-Microsservi%C3%A7os/dp/6586057043'
]

const validatingIsbn = (isbns, links) => {
    let invalidos = {}, validos = {}
    return isbns.reduce((obj, isbn, index) => {
        let result 
        if (links[index] == `Nenhum resultado para ${[isbn]}.`) {
            let invalido = Object.assign(invalidos, {[isbn] : links[index]})
            result = {...obj, invalido}
        } else {
            let valido = Object.assign(validos, {[isbn] : links[index]})
            result = {...obj, valido}
        }
        return result
    }, {})
}

console.log(validatingIsbn(isbns, links))

Answer 1

Best practice to use reduce is: do not use reduce where it is not appropriate to use that method.

reduce is a very flexible method, you can use it to create new arrays, create objects, filter elements, apply mathematical operations, but the method is not very idiomatic for most of these uses (the last being the exception).

Using it to calculate the total values contained in an object array is simple and idiomatic, you might even call it elegant. Use it to create an object indexed with array values, not so much, no readability gains or lines of code.

So, my suggestion, something totally subjective and not applicable the answer of this site, but what I’m giving anyway, is not using the reduce for these scenarios.

And here’s a hint of how to refactor function to a way that I see as more readable:

function validatingIsbn(isbns, links) {
    const validos = {}, invalidos = {};

    for (let i = 0; i < links.length; i++) {
        const categoria = links[i] === `Nenhum resultado para ${isbns[i]}` ? invalidos : validos;
        categoria[isbns[i]] = links[i];
    }

    return { validos, invalidos };
}