Question

How to sort this object lexicographically by its keys:

var obj = {'somekey_B' : 'itsvalue', 'somekey_A' : 'itsvalue');

so that it outputs like this:

for (k in obj) {
  alert(k + ' : ' + obj[k]); //first "somekey_A : itsvalue"; then "somekey_B : itsvalue"
}

Answer 1

You can’t. The order in which for..in loops through the property names is implementation-specific and cannot be controlled. Your only alternative is to organize the properties yourself in some way, such as building an array of keys and then sorting it, e.g.:

var keys, index;

keys = [];
for (k in obj) {
    keys.push(k);
}
keys.sort();
for (index = 0; in dex < keys.length; ++index) {
  k = keys[index];
  alert(k + ' : ' + obj[k]); //first "somekey_A : itsvalue"; then "somekey_B : itsvalue"
}

You could, of course, put that in a function on the object and use it to iterate through the keys. Alternately, you could keep a sorted array on the object itself, provided you kept it up-to-date when you created new properties.