JavaScript - why Array.prototype.fill actually fills a “pointer” of object when filling anything like 'new Object()'

Question

I was trying to used Array.prototype.fill method to create a n x n 2D array but the code was buggy and I eventually found out all arrays inside are actually

Answer 1

With recursion you can make even more dimensions ;)

const range = r => Array(r).fill().map((v, i) => i);
const range2d = (x, y) => range(x).map(i => range(y));
const rangeMatrix = (...ranges) => (function ranger(ranged) {
  return ranges.length ? ranger(range(ranges.pop()).map(i => ranged)) : ranged
})(range(ranges.pop()));

let arr10x10 = range2d(10, 10);
let arr3x5 = range2d(3, 2);
let arr4x3 = rangeMatrix(4, 3);
let arr4x3x2 = rangeMatrix(4, 3, 2);
let arr4x3x2x5 = rangeMatrix(4, 3, 2, 5);

console.log(arr10x10);
console.log(arr3x5);
console.log(arr4x3);
console.log(arr4x3x2);
console.log(arr4x3x2x5);