I am creating a map of array using this:
var m = new Map(Array(40).fill(new Array()).entries()); Now, I want to push values in those array. But when I do this:
m.get(1).push(10) The value 10 gets pushed into all the arrays instead of the one at 1st position.
You could take another pattern to build independent arrays.
var m = new Map(Array.from({ length: 40 }, _=> []).entries()); m.get(1).push(10); console.log([...m]);fill gets single array an uses it to fill all rows of the given array, it doesn't create a new array for each row. This means that your single array reference is shared between all rows. Because array is a reference type, you use the single reference to manipulate it, so the actual object is changed. You can check this by comparing the references of each row.
const arr = new Array(2).fill(new Array()); console.log(arr[0] === arr[1]);For creating separate arrays, you can see @Nina's answer above
