Question

Can I depend on the following code alerting b before a?

var x = {}
x['b'] = 1
x['a'] = 0
for(var i in x) {
    alert(i)
}

Answer 1

For the V8 JavaScript engine used in Google Chrome, a similar discussion took place:

http://code.google.com/p/v8/issues/detail?id=164

It’s better to not rely on undocumented features. And it you’re using numbers as keys, it certainly goes wrong.

For example this breaks in some browsers:

var x = {}
x['b'] = 1
x['2'] = 20
x['a'] = 0
x['1'] = 10
for(var i in x) {
    alert(x[i])
}

BTW it’s alert(x[i]).