Number of elements in a javascript object

Question

Is there a way to get (from somewhere) the number of elements in a javascript object?? (i.e. constant-time complexity).

I cant find a property or method that retriev

Answer 1

To do this in any ES5-compatible environment

Object.keys(obj).length

(Browser support from here)
(Doc on Object.keys here, includes method you can add to non-ECMA5 browsers)