Throw when non-existent property is read

lib/chai/assertion.js

@@ -33,6 +33,8 @@ module.exports = function (_chai, util) {
     flag(this, 'ssfi', stack || Assertion);
     flag(this, 'object', obj);
     flag(this, 'message', msg);
+
+    return util.proxify(this);
   }
 
   Object.defineProperty(Assertion, 'includeStack', {

lib/chai/core/assertions.js

@@ -300,7 +300,7 @@ module.exports = function (chai, _) {
         true === flag(this, 'object')
       , 'expected #{this} to be true'
       , 'expected #{this} to be false'
-      , this.negate ? false : true
+      , flag(this, 'negate') ? false : true
     );
   });
 
@@ -322,7 +322,7 @@ module.exports = function (chai, _) {
         false === flag(this, 'object')
       , 'expected #{this} to be false'
       , 'expected #{this} to be true'
-      , this.negate ? true : false
+      , flag(this, 'negate') ? true : false
     );
   });
 
@@ -1528,7 +1528,7 @@ module.exports = function (chai, _) {
         result
       , 'expected #{this} to satisfy ' + _.objDisplay(matcher)
       , 'expected #{this} to not satisfy' + _.objDisplay(matcher)
-      , this.negate ? false : true
+      , flag(this, 'negate') ? false : true
       , result
     );
   }

lib/chai/utils/addChainableMethod.js

@@ -10,6 +10,7 @@
 
 var transferFlags = require('./transferFlags');
 var flag = require('./flag');
+var proxify = require('./proxify');
 
 /*!
  * Module variables
@@ -104,7 +105,7 @@ module.exports = function (ctx, name, method, chainingBehavior) {
         }
 
         transferFlags(this, assert);
-        return assert;
+        return proxify(assert);
       }
     , configurable: true
   });

lib/chai/utils/index.js

@@ -152,3 +152,9 @@ exports.getOwnEnumerableProperties = require('./getOwnEnumerableProperties');
  */
 
 exports.checkError = require('check-error');
+
+/*!
+ * Proxify util
+ */
+
+exports.proxify = require('./proxify');

lib/chai/utils/proxify.js

@@ -0,0 +1,35 @@
+/*!
+ * Chai - proxify utility
+ * Copyright(c) 2012-2014 Jake Luer <jake@alogicalparadox.com>
+ * MIT Licensed
+ */
+
+/**
+ * # proxify(object)
+ *
+ * Return a proxy of given object that throws an error when a non-existent
+ * property is read. (If Proxy or Reflect is undefined, then return object
+ * without modification.)
+ *
+ * @param {Object} obj
+ * @namespace Utils
+ * @name proxify
+ */
+
+module.exports = function proxify (obj) {
+  if (typeof Proxy === 'undefined' || typeof Reflect === 'undefined')
+    return obj;
+
+  return new Proxy(obj, {
+    get: function getProperty (target, property) {
+      // Don't throw error on Symbol properties such as Symbol.toStringTag, nor
+      // on .then because it's necessary for promise type-checking.
+      if (typeof property === 'string' &&
+          property !== 'then' &&
+          !Reflect.has(target, property))
+        throw Error('Invalid Chai property: ' + property);
+
+      return target[property];
+    }
+  });
+};

test/expect.js

@@ -10,6 +10,31 @@ describe('expect', function () {
     expect('foo').to.equal('foo');
   });
 
+  it('invalid property', function () {
+    if (typeof Proxy === 'undefined' || typeof Reflect === 'undefined') return;
+
+    err(function () {
+      expect(42).pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      expect(42).to.pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      expect(42).to.be.a.pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      expect(42).to.equal(42).pizza;
+    }, 'Invalid Chai property: pizza');
+
+    // .then is excluded from property validation for promise support
+    expect(function () {
+      expect(42).then;
+    }).to.not.throw();
+  });
+
   it('no-op chains', function() {
     function test(chain) {
       // tests that chain exists

test/should.js

@@ -7,6 +7,31 @@ describe('should', function() {
     should.not.equal('foo', 'bar');
   });
 
+  it('invalid property', function () {
+    if (typeof Proxy === 'undefined' || typeof Reflect === 'undefined') return;
+
+    err(function () {
+      (42).should.pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      (42).should.be.pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      (42).should.be.a.pizza;
+    }, 'Invalid Chai property: pizza');
+
+    err(function () {
+      (42).should.equal(42).pizza;
+    }, 'Invalid Chai property: pizza');
+
+    // .then is excluded from property validation for promise support
+    (function () {
+      (42).should.then;
+    }).should.not.throw();
+  });
+
   it('no-op chains', function() {
     function test(chain) {
       // tests that chain exists

test/utilities.js

@@ -844,4 +844,39 @@ describe('utilities', function () {
       expect(gettem(obj)).to.have.same.members([cat, dog, bird]);
     });
   });
+
+  describe('proxified object', function () {
+    if (typeof Proxy === 'undefined' || typeof Reflect === 'undefined') return;
+
+    var proxify;
+
+    beforeEach(function () {
+      chai.use(function (_chai, _) {
+        proxify = _.proxify;
+      });
+    });
+
+    it('returns property value if an existing property is read', function () {
+      var pizza = proxify({mushrooms: 42});
+
+      expect(pizza.mushrooms).to.equal(42);
+    });
+
+    it('throws error if a non-existent property is read', function () {
+      var pizza = proxify({});
+
+      expect(function () {
+        pizza.mushrooms;
+      }).to.throw('Invalid Chai property: mushrooms');
+    });
+
+    // .then is excluded from property validation for promise support
+    it('doesn\'t throw error if non-existent `then` is read', function () {
+      var pizza = proxify({});
+
+      expect(function () {
+        pizza.then;
+      }).to.not.throw();
+    });
+  });
 });