Ordered hash in JavaScript

Question

JavaScript objects have no order stored for properties (according to the spec). Firefox seems to preserve the order of definition of properties when using a for...in<

Answer 1

A fairly simple way is to use an array to store the order. You need to write a custom compare function to establish the order you require. The down side is that you have to sort the array and keep track of relations, each time you change the hash table.

var order=[];
var hash={"h1":4,"h2":2,"h3":3,"h4":1};

function cmp(a,b) {
  if (hash[a] < hash[b]) return -1;
  if (hash[a] > hash[b]) return 1;
  return 0;
}

// Add initial hash object to order array
for(i in hash) order.push(i);
order.sort(cmp);
// h4:1 h2:2 h3:3 h1:4

// Add entry
hash['h5']=2.5;
order.push('h5');
order.sort(cmp);
// h4:1 h2:2 h5:2.5 h3:3 h1:4

// Delete entry
order.splice(order.indexOf('h5'), 1);
delete hash['h5'];
// h4:1 h2:2 h3:3 h1:4

// Display ordered hash array (with keys)
for(i in order) console.log(order[i],hash[order[i]]);