Make proxies optional

lib/chai/config.js

@@ -50,6 +50,25 @@ module.exports = {
    * @api public
    */
 
-  truncateThreshold: 40
+  truncateThreshold: 40,
 
+  /**
+   * ### config.useProxy
+   *
+   * User configurable property, defines if chai will use a Proxy to throw
+   * an error when a non-existent property is read, which protects users
+   * from typos when using property-based assertions.
+   *
+   * Set it to false if you want to disable this feature.
+   *
+   *     chai.config.useProxy = false;  // disable use of Proxy
+   *
+   * This feature is automatically disabled regardless of this config value
+   * in environments that don`t support proxies.
+   *
+   * @param {Boolean}
+   * @api public
+   */
+
+  useProxy: true
 };

lib/chai/utils/proxify.js

@@ -1,3 +1,5 @@
+var config = require('../config');
+
 /*!
  * Chai - proxify utility
  * Copyright(c) 2012-2014 Jake Luer <jake@alogicalparadox.com>
@@ -17,7 +19,7 @@
  */
 
 module.exports = function proxify (obj) {
-  if (typeof Proxy === 'undefined' || typeof Reflect === 'undefined')
+  if (!config.useProxy || typeof Proxy === 'undefined' || typeof Reflect === 'undefined')
     return obj;
 
   return new Proxy(obj, {

test/configuration.js

@@ -1,5 +1,6 @@
 describe('configuration', function () {
   var assert = chai.assert;
+  var expect = chai.expect;
 
   var origConfig;
 
@@ -73,7 +74,6 @@ describe('configuration', function () {
           assert.include(err.stack, 'fooPropThrows', 'should have user stack trace in error message');
         }
       }
-
     });
 
     it('is false for property assertions', function () {
@@ -167,6 +167,33 @@ describe('configuration', function () {
       chai.config.showDiff = !chai.config.showDiff;
       assert.equal(chai.Assertion.showDiff, chai.config.showDiff);
     });
-
+  });
+
+  describe('useProxy', function() {
+    var readNoExistentProperty = function() {
+      expect(false).to.be.tue; // typo: tue should be true
+    };
+
+    it('should have default value equal to true', function() {
+      expect(chai.config.useProxy).to.be.true;
+    });
+
+    describe('when true', function() {
+      it('should use proxy unless user\'s environment doesn\'t support', function() {
+        if (typeof Proxy !== 'undefined' && typeof Reflect !== 'undefined') {
+          expect(readNoExistentProperty).to.throw('Invalid Chai property: tue');
+        } else {
+          expect(readNoExistentProperty).to.not.throw('Invalid Chai property: tue');
+        }
+      });
+    });
+
+    describe('when false', function() {
+      it('should not use proxy', function() {
+        chai.config.useProxy = false;
+
+        expect(readNoExistentProperty).to.not.throw('Invalid Chai property: tue');
+      });
+    });
   });
 });