Javascript Object Big-O

Coming from Java, Javascript object reminds me of HashMap in Java.

Javascript:

var myObject = {
    firstName: "Foo",
    lastName: "Bar",
    email: "foo@bar.com"
};

Java:

HashMap<String, String> myHashMap = new HashMap<String, String>();
myHashMap.put("firstName", "Foo");
myHashMap.put("lastName", "Bar");
myHashMap.put("email", "foo@bar.com");

In Java HashMap, it uses the hashcode() function of the key to determine the bucket location (entries) for storage, and retrieval. Majority of the time, for basic operations such as put() and get(), the performance is constant time, until a hash collision occurs which becomes O(n) for these basic operations because it forms a linked list in order to store the collided entries.

My question is:

1. How does Javascript stores object?


2. What is the performance of operations?


3. Will there ever be any collision or other scenarios which will degrade the performance like in Java

Thanks!