javascript - Complexity of accessing data in an object

Question

In some of the projects I'm working on as part of my day job, I need to access data in very large JS objects (on the order of thousands of key-value pairs). I'm trying to improve the efficiency of my code, so I came up with a few questions:

1. What is the runtime complexity of JS when accessing a field in such an object? My initial hunch is that it's O(n)
2. Is there a difference when accessing through dot notation or bracket notation? (e.g. obj.field vs obj[field])
3. I'm guessing there is a different answer for different runtime engines - is there a place where I can see the difference between them?

Answer 1

Javascript objects are actually Hashes, so the complexity is O(1) for all engines.

obj.field is an alias for obj['field'], so they have the same performances.

You can find some JS hashes performance tests here, unfortunately only for your browser engine.