unique object identifier in javascript

Question

I need to do some experiment and I need to know some kind of unique identifier for objects in javascript, so I can see if they are the same. I don't want to use equality operators, I need something like the id() function in python.

Does something like this exist ?

Answer 1

<script type="text/javascript">
if (Object.prototype != undefined || Object.prototype != null) {
    // This is generally not a good practice as onwards
    // this function will going to be attached
    // to all native/user defined objects. i.e.
    // object create with {}, [], new etc.
    Object.prototype.uniqueID = function() {
            return Math.floor(Math.random() * 1000);
    }
}
var obj1 = {};
var obj2 = new Object();

alert(obj1.uniqueID());
alert(obj2.uniqueID());
alert([].uniqueID());
alert({}.uniqueID());
</script>

Answer 2

You can give the following a spin. This also gives you the option to explicitly set an object's ID in its constructor or elsewhere.

(function() {
    if ( typeof Object.prototype.uniqueId == "undefined" ) {
        var id = 0;
        Object.prototype.uniqueId = function() {
            if ( typeof this.__uniqueid == "undefined" ) {
                this.__uniqueid = ++id;
            }
            return this.__uniqueid;
        };
    }
})();

var obj1 = {};
var obj2 = new Object();

console.log(obj1.uniqueId());
console.log(obj2.uniqueId());
console.log([].uniqueId());
console.log({}.uniqueId());
console.log(/./.uniqueId());
console.log((function() {}).uniqueId());

Take care to make sure that whatever member you use to internally store the unique ID doesn't collide with another automatically created member name.

Answer 3

jQuery code uses it's own data() method as such id.

var id = $.data(object);

At the backstage method data creates a very special field in object called "jQuery" + now() put there next id of a stream of unique ids like

id = elem[ expando ] = ++uuid;

I'd suggest you use the same method as John Resig obviously knows all there is about JavaScript and his method is based on all that knowledge.

Answer 4

If you want to include all objects, including those defined using a special literal syntax (such as {}, [], /regex/, functions, ...), then no.

That is . . . unless you are willing to manually generate an id for every object you create and for every built-in/imported object:

var genId, getId, genIdRecursive;

(function () {
  var hiddenProps = [
      "prototype"
    , "toString"
    , "length"
    , ">>> REPLACE ME WITH ALL OTHER PROPS FOR-IN DOESN'T LOOP OVER! <<<"
    ];

  function isObj (x) {
    var type = typeof x
    return x !== null && (type === "object" || type === "function");
  }

  var idProp = "%*genId.idProp*%";
  var currId = 1 << 31;
  var maxId = -((1 << 31) + 1);

  genId = function () {
    for (var i = 0; i < arguments.length; ++i) {
      if (currId >= maxId) {
        return Math.random ();
      }
      var arg = arguments [i];
      if (isObj (arg)) {
        arg [idProp] = currId++;
      }
    }
  }

  getId = function (obj) {
    var id = obj [idProp];
    return id === undefined ? null : id;
  }

  genIdRecursive = function () {
    for (var i = 0; i < arguments.length; ++i) {
      var arg = arguments [i];
      if (!isObj (arg)) {
        continue;
      }
      try {
        if (getId (arg) !== null) {
          continue;
        }
        genId (arg);
      }
      catch (e) {
        continue;
      }
      var props = [];
      for (var prop in arg) {
         props.push (prop);
      }
      var nPs = props.length;
      var nHs = hiddenProps.length;
      var n = nHs + nPs;
      for (var i = 0; i < n; ++i) {
        var prop = i < nHs
          ? hiddenProps [i]
          : props [i - nHs]
          ;
        var val;
        try {
          val = arg [prop];
        }
        catch (e) {
          continue;
        }
        genIdRecursive (val);
      }
    }
  };

  genId (genId, getId, genIdRecursive);
}) ();

---

Examples:

function func1 () {}
genId (func1);

var func2 = genId (function () {});

var xs = genId (["array literal"]);

var regex = genId (/regex/);

var foo = genId ({ foo: "foo" });

var bar = genId (new Bar ());

Answer 5

I've used code like this, which will cause Objects to stringify with unique strings:

Object.prototype.__defineGetter__('__id__', function () {
    var gid = 0;
    return function(){
        var id = gid++;
        this.__proto__ = {
             __proto__: this.__proto__,
             get __id__(){ return id }
        };
        return id;
    }
}.call() );

Object.prototype.toString = function () {
    return '[Object ' + this.__id__ + ']';
};

the __proto__ bits are to keep the __id__ getter from showing up in the object. this has been only tested in firefox.