Why this code references different result

Question

I am new to JS and was learning value and reference types in JS but I faced some confusion on the below code:

Answer 1

const obj = {
 arr: [{ x: 17 }]
};

/**
 * z -> it is only reference to original object (const obj in our case). 
 * It is like another door to the same room
 */
let z = obj.arr;

/*
 * now z -> points to other value (array), but previous still exist
 */
z = [{ x: 25 }]; 

console.log(obj.arr[0].x);