Sorting a JavaScript object by property name

UPDATE from the comments:

This answer is outdated. In ES6 objects keys are now ordered. See this question for an up-to-date answer

By definition, the order of keys in an object is undefined, so you probably won't be able to do that in a way that is future-proof. Instead, you should think about sorting these keys when the object is actually being displayed to the user. Whatever sort order it uses internally doesn't really matter anyway.

By convention, most browsers will retain the order of keys in an object in the order that they were added. So, you could do this, but don't expect it to always work:

function sortObject(o) {
    var sorted = {},
    key, a = [];

    for (key in o) {
        if (o.hasOwnProperty(key)) {
            a.push(key);
        }
    }

    a.sort();

    for (key = 0; key < a.length; key++) {
        sorted[a[key]] = o[a[key]];
    }
    return sorted;
}

this function takes an object and returns a sorted array of arrays of the form [key,value]

function (o) {
   var a = [],i;
   for(i in o){ 
     if(o.hasOwnProperty(i)){
         a.push([i,o[i]]);
     }
   }
   a.sort(function(a,b){ return a[0]>b[0]?1:-1; })
   return a;
}

The object data structure does not have a well defined order. In mathematical terms, the collection of keys in an object are an Unordered Set, and should be treated as such. If you want to define order, you SHOULD use an array, because an array having an order is an assumption you can rely on. An object having some kind of order is something that is left to the whims of the implementation.

Just use sorted stringify() when you need to compare or hash the results.