Javasript array functions with no arguments [duplicate]

Question

This is more like a silly question but I have to ask it. It is a good practice to call an array function like map without arguments? Let's say I already have an array 'x' on my code with a specified length and I want to make another array with the same length but with different content. For example:

function generateRandomContent() { ... }
const x = [1, 2, 3, 4, 5]
const y = x.map(() => generateRandomContent())
// or
const z = Array(x.length).fill().map(() => { ... })

Of course I could pass an argument and never use it, but it is there a good way and a bad way to do it?

Why would you want to do a mapping operation if it's not dependent on anything but the size of the initial array? — VLAZ
– VLAZ, Commented Dec 27, 2019 at 14:45
.map() is not supposed to be used without arguments. You could use .forEach() instead or a for loop. — Yousername
– Yousername, Commented Dec 27, 2019 at 14:45
Array.from({length: x.length}, () => someFn()) or even Array.from({length: x.length}, someFn) will generate an array as the same size with different contents. .map signifies that the content of the new array is closely related to the content of the original array. — VLAZ
– VLAZ, Commented Dec 27, 2019 at 14:47
Maybe it's worth considering Array.from, which takes a function as its second argument. E.g.: Array.from(Array(10), generateRandomContent). — user3297291
– user3297291, Commented Dec 27, 2019 at 14:48

VLAZ · Accepted Answer · 2019-12-27 14:59:20Z

You should not use .map here. A mapping operation is when you take some input and generate a new output. So you have a relation that looks like this x -> y for a single element, then you apply it to the entire array to generate a new array using the same mapping rule:

const input = [104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100];

//mapping relationship
const toCharacter = x => String.fromCharCode(x);

const result = input.map(toCharacter);

console.log(result.join(''))

If you just want to create a new array based on the length of the original but with totally unrelated content, then you are better off to use Array.from which can create an array with a given size and takes a second argument that will fill it with content:

function generateRandomContent() {
  return Math.floor(Math.random() * 100);
}
const x = [1, 2, 3, 4, 5]

const y = Array.from({length: x.length}, () => generateRandomContent());
//or just pass the function reference
const z = Array.from({length: x.length}, generateRandomContent);


console.log(y);
console.log(z);

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