// x = [7,2]
let x = [7, 2];
// y = [[7,2]]
let y = [x]
// x = [9,2]
x[0] = 9;
// y also = [[9,2]]
console.log(y);Why is it that when I changed x, y changed as well? Shouldn't y still be what it was when I initialized it [[7,2]]? What is this phenomenon called?
In javascript when you copy over array to another variable, it does not copy over the data to another variable. It will create a reference to that variable, so when the original array changes, copied over array would also change this is called as call by reference.
Another term is called as call by value which will copy over the data to another variable, which is the case for primitive data types
Copying value by reference. - https://www.dyn-web.com/javascript/arrays/value-vs-reference.php
What you want to do instead -
let x = [7,2];
let y = [...x];
x[0] = 9;
(2) [9, 2]
y
(2) [7, 2]
