JS: x.y.z Associativity, Right or Left?

fun JavaScript problem. Test your knowledge.

// what's the value of x.y.z()

const x = {
    "y.z":function () { return 4;},
    "y":{"z":function () { return 3;}}
};

console.log(x.y.z());

Try it out in your browser console to see the answer. [see JS: How to Use Browser Console]