fix for issue #25 when updating a property

reflect.js

@@ -366,10 +366,10 @@ function isFixed(name, target) {
 function isSealed(name, target) {
   var desc = Object.getOwnPropertyDescriptor(target, name);
   if (desc === undefined) { return false; }
-  return !desc.configurable;
+  return desc.configurable === false;
 }
 function isSealedDesc(desc) {
-  return desc !== undefined && !desc.configurable;
+  return desc !== undefined && desc.configurable === false;
 }
 
 /**
@@ -544,7 +544,7 @@ Validator.prototype = {
       }
     }
 
-    if (!desc.configurable && !isSealedDesc(targetDesc)) {
+    if (desc.configurable === false && !isSealedDesc(targetDesc)) {
       // if the property is configurable or non-existent on the target,
       // but is reported as a non-configurable property, it may later be
       // reported as configurable or non-existent, which violates the
@@ -668,7 +668,7 @@ Validator.prototype = {
         }
       }
 
-      if (!desc.configurable && !isSealedDesc(targetDesc)) {
+      if (desc.configurable === false && !isSealedDesc(targetDesc)) {
         // if the property is configurable or non-existent on the target,
         // but is successfully being redefined as a non-configurable property,
         // it may later be reported as configurable or non-existent, which violates

test/testProxies.js

@@ -98,6 +98,7 @@ load('../reflect.js');
       testRevocableProxies();
       testSetPrototypeOf();
       testSetPrototypeOfUndefined();
+      testUpdatePropertyDescriptor();
       //testInvokeTrap();
 
       for (var testName in TESTS) {
@@ -820,7 +821,21 @@ load('../reflect.js');
     } catch (ex) {
       shouldThrow = ex;
     }
-    assert(shouldThrow);
+    assert(shouldThrow, 'testSetPrototypeOfUndefined: cannot set to undefined');
+  }
+
+  function testUpdatePropertyDescriptor() {
+    var obj = {};
+    Object.defineProperty(obj, 'prop', {value: true, configurable: true});
+    var proxy = Proxy(obj, {
+      defineProperty: function(target, name, desc) {
+        return Object.defineProperty(obj, name, desc);
+      }
+    });
+    Object.defineProperty(proxy, 'prop', {value: function() { return false; }});
+    var descriptor = Object.getOwnPropertyDescriptor(obj, 'prop');
+    assert(typeof descriptor.value === 'function',
+           'testUpdatePropertyDescriptor: prop updated');
   }
 
   // invoke experiment