关于“函数调用其他函数”的问题

Question

enter image description here

const percentageOfWorld2 = function (population) {
   return (population / 7900) * 100
};

let Koreapl = percentageOfWorld2(52);
let Japanpl = percentageOfWorld2(60);
let Chinapl = percentageOfWorld2(1441);

console.log(Koreapl, Japanpl, Chinapl);

const describePopulation = function (country, population) {
    return `${country} has ${population} million people, which is about ${percentageOfWorld2(population)}% of the world`
}
console.log(describePopulation('korea', 52));
console.log(describePopulation('Japan', 60));
console.log(describePopulation('China', 1441));

Hello.I'm new at coding world,And I've been working on this code. and the image that I put on is the answer for this code, Either way I've got the same result. with my code and the answer, I get that above one is better but could anyone explain more, why it's better to declare the const variables into the function?without just returning like what I did in my answer?

Answer 1

If this version is your function:

const describePopulation = function (country, population) {
    return `${country} has ${population} million people, which is about ${percentageOfWorld2(population)}% of the world`
}

then I like your answer better than the "correct" answer. It depends on what describePopulation is supposed to do. Is it supposed to both compute a description, and then, as a side effect, display that description to the console? Or, is it simply meant to compute a description?

IMHO, a function should do only one thing, and do that one thing well. I prefer the implementation where describePopulation is meant to compute a description, and it is left for some other function to output that to the console. So, I like your version better.

As to using a variable only once, as someone mentioned in a comment, one very important aspect of programming is to make your code readable. Code is read much, much more than it is written. Code is typically modified many, many times over its lifetime. Anything you can do to make your code easy to read and easy to understand at a glance is good. This includes using what others may view as "pointless" variables. They are not pointless if they make the meaning of what you are reading leap from the screen.