Nodejs Order of properties guarantee - node.js

Question

Note: I am using Nodejs which may or may not have subtle differences from vanilla ECMAscript's standards.
I have always heard that when using a for-each loop to iterate over the properties of an object, I should not count on the properties being in the same order. (even though in practice I have never seen a case where the objects were iterated over in a different order). In production, we have what I believe to be a typo where an object is created with an overwritten property.
var obj = {
a: 'a property',
b: 'another property',
c: 'yet another property',
a: 'woah we have another a?'
}
In Nodejs, am I guaranteed that the second a property containing the string 'woah we have another a?' will ALWAYS shadow the first a property containing the string 'a property'?

Answer 1

(even though in practice I have never seen a case where the objects were iterated over in a different order)
The following should give you a different order in V8 atleast.
var obj = {
"first":"first",
"2":"2",
"34":"34",
"1":"1",
"second":"second"
};
for (var i in obj) { console.log(i); };
// Order listed:
// "1"
// "2"
// "34"
// "first"
// "second"
As discussed here
ECMA-262 does not specify enumeration order. The de facto standard is to match
insertion order, which V8 also does, but with one exception:
V8 gives no guarantees on the enumeration order for array indices (i.e., a property
name that can be parsed as a 32-bit unsigned integer).
Remembering the insertion order for array indices would incur significant memory
overhead.
Though the above says the enumeration order is not specified but that is after the object is created. I think we can safely assume that insertion order should remain consistent, as there is no point for any engine to do otherwise and alter the insertion order.
var obj = {
"first":"first",
"2":"2",
"34":"34",
"1":"1",
"second":"second",
2: "two"
};
// gives result
{ '1': '1',
'2': 'two',
'34': '34',
first: 'first',
second: 'second' }