Javascript - maintain key order when going from object -> array

Question

I know key order isn\'t guaranteed in JS objects, however, my data structure comes from a backend for which I have no control over. Is there anything I can do to preserve th

Answer 1

ECMA-262 does not specify enumeration order. The de facto standard is to match insertion order.

No guarantees are given though on the enumeration order for array indices (i.e., a property name that can be parsed as an integer), because insertion order for array indices would incur significant memory overhead.

EDIT: added jsfiddle example.

var obj1 = {
   a: 'test1',
   b: 'test2' 
};

var obj2 = {
   2: 'test1',
   1: 'test2' 
};
// max 32bit unsigned is 2,147,483,647
var obj3 = {
   2147483649: 'test1',
   2147483648: 'test2' 
};
// max 64bit unsigned is 9,223,372,036,854,775,807
var obj4 = {
   9223372036854770: 'test1',
   9223372036854768: 'test2',
};

// != number < 2,147,483,647, order is not changed
console.log(Object.keys(obj1));
// < 2,147,483,647, order is changed
console.log(Object.keys(obj2));
// > 2,147,483,647, order is not changed in Firefox, but changed in Chrome
console.log(Object.keys(obj3));
// > 9,223,372,036,854,775,807, order is not changed in neither Firefox or Chrome
console.log(Object.keys(obj4));

Which means Chrome's javascript engine V8 will order any 64bit unsigned numbers, while Firefox's javascript engine SpiderMonkey will order any 32bit unsigned numbers.