JavaScript Hashtable for Objects

JavaScript…

there comes a time in every developer’s life when he wishes to be able to use a Hash in JavaScript like he can use a Hash in Ruby, you know, easily. This usually comes up when implementing A* or some other crazy graph search algorithm.

The problem: JavaScript objects make great Hashes for String and Number keys, but not for Object keys. Some QUnit tests highlight the problem readily.

    test("Hash sux?", function() {
      var x = {};
      var y = {name: "My Cool Object"};
      var barbazfoo = {name: "My Uncool Object"};

      x['a'] = true;
      x['b'] = true;

      equals(x['a'], true);
      equals(x['b'], true);

      x[y] = y.name;
      x[barbazfoo] = barbazfoo.name;

      equals(x[y], y.name); // Failed! y.toString == "[object Object]"
      equals(x[barbazfoo], barbazfoo.name);
    });

Now we have two options as I see it: download (or hand roll) our own Hashtable class that has even more akward syntax, worse performance and clocks in at 5k minified… or implement a toString() method that generates unique strings for each object (of types that we care about).

I opted for the second choice, after coming very close to choosing the first. Now if only there were some magical way to implement a unique toString method for all my objects that might want to end up as hash keys.

(function() {
    var id = 0;

    /*global GameObject */
    GameObject = function(game) {
      var self = {
        // Empty update by default
        update: function() {},
        click: function() {},
        objectId: '#Object:' + (id++),
        toString: function() {
          return self.objectId;
        }
      };
      return self;
    };
  })();

Gerta Rauss: So, we all agree that a closure is the best decision for all involved?

Juno MacGuff: SSHHIT! YES! Closure it up!

Now any GameObject can be used as a key to a hash, and as long as you aren’t going nuts and mixing and matching crazy strings as your keys you should have no collisions, or at least way fewer than 100%. Thanks a heap ‘[object Object]’!.

Author: Daniel X

Heretic priest of the Machine God. I enjoy crawling around in Jeff Bezo's spaceship, bringing technology to the people, and long walks outside of time and space. View all posts by Daniel X