Add WeakMap.has and conform WeakMap.delete to spec

tests/index.html

@@ -24,15 +24,16 @@
 <!-- Tests -->
 <script>
   suite('WeakMap', function() {
-
     var assert = chai.assert;
 
-    test('WeakMap has get and set functions', function() {
+    test('WeakMap has get, set, delete, and has functions', function() {
       assert.isDefined(WeakMap.prototype.get);
       assert.isDefined(WeakMap.prototype.set);
+      assert.isDefined(WeakMap.prototype.delete);
+      assert.isDefined(WeakMap.prototype.has);
     });
 
-    test('WeakMap\'s get and set perform as expected', function() {
+    test('WeakMap\'s methods perform as expected', function() {
       var wm = new WeakMap();
 
       var o1 = {};
@@ -54,6 +55,16 @@
       assert.equal(wm.get({}), undefined);
       // `wm.get(o3)` should return undefined, because that is the set value
       assert.equal(wm.get(o3), undefined);
+
+      assert.equal(wm.has(o1), true);
+      assert.equal(wm.has({}), false);
+
+      wm.delete(o1);
+      assert.equal(wm.get(o1), undefined);
+      assert.equal(wm.has(o1), false);
+      // Ensure that delete returns true/false indicating if the value was removed
+      assert.equal(wm.delete(o2), true);
+      assert.equal(wm.delete({}), false);
     });
   });
 </script>

weakmap.js

@@ -27,7 +27,16 @@ if (typeof WeakMap === 'undefined') {
             entry[1] : undefined;
       },
       delete: function(key) {
-        this.set(key, undefined);
+        var entry = key[this.name];
+        if (!entry) return false;
+        var hasValue = entry[0] === key;
+        entry[0] = entry[1] = undefined;
+        return hasValue;
+      },
+      has: function(key) {
+        var entry = key[this.name];
+        if (!entry) return false;
+        return entry[0] === key;
       }
     };