JS Arrays are By Reference by default

arraysbyref.js

const a = [0, 1, 2, 3];
const b = a;
b.push(10);
console.log(b); // [0, 1, 2, 3, 10]
console.log(a); // [0, 1, 2, 3, 10] (10 got pushed to a even though we only pushed to b)

// To AVOID passing by reference
const foo = [0, 1, 2, 3];
const bar = foo.concat([10]);
console.log(bar); // [0, 1, 2, 3, 10]
console.log(foo); // [0, 1, 2, 3] (10 did not get pushed here)