feat(bindPromiseFn): add bindPromiseFn method

Closes #49

Author: btford

Diff for: karma.conf.js

@@ -4,10 +4,10 @@ module.exports = function (config) {
   config.set({
     basePath: '',
     files: [
+      'test/util.js',
       'zone.js',
       '*-zone.js',
       //'test/lib/brick.js',
-      'test/util.js',
       'test/**/*.spec.js',
       {pattern: 'test/assets/**/*.html', watched: true, served: true, included: false}
     ],

Diff for: test/util.js

@@ -21,3 +21,6 @@ function ifEnvSupports(test, block) {
     }
   };
 };
+
+// useful for testing mocks
+window.__setTimeout = window.setTimeout;

Diff for: test/zone.spec.js

@@ -140,6 +140,32 @@ describe('Zone', function () {
     });
   });
 
+  describe('bindPromiseFn', function () {
+    var mockPromise = function() {
+      return {
+        then: function (a, b) {
+          window.__setTimeout(a, 0);
+          return mockPromise();
+        }
+      };
+    };
+
+    it('should return a method that returns promises that run in the correct zone', function (done) {
+      zone.fork({ mark: 'a' }).run(function () {
+        var patched = Zone.bindPromiseFn(function() {
+          return mockPromise();
+        });
+
+        patched().then(function () {
+          expect(zone.mark).toBe('a');
+        }).then(function () {
+          expect(zone.mark).toBe('a');
+          done();
+        });
+      });
+    });
+  });
+
 });
 
 function throwError () {

Diff for: zone.js

@@ -221,6 +221,52 @@ Zone.bindArgumentsOnce = function (args) {
   return args;
 };
 
+/*
+ * patch a fn that returns a promise
+ */
+Zone.bindPromiseFn = (function() {
+  // if the browser natively supports Promises, we can just return a native promise
+  if (window.Promise) {
+    return function (delegate) {
+      return function() {
+        var delegatePromise = delegate.apply(this, arguments);
+        if (delegatePromise instanceof Promise) {
+          return delegatePromise;
+        } else {
+          return new Promise(function(resolve, reject) {
+            delegatePromise.then(resolve, reject);
+          });
+        }
+      };
+    };
+  } else {
+    // if the browser does not have native promises, we have to patch each promise instance
+    return function (delegate) {
+      return function () {
+        return patchThenable(delegate.apply(this, arguments));
+      };
+    };
+
+    function patchThenable(thenable) {
+      var then = thenable.then;
+      thenable.then = function () {
+        var args = Zone.bindArguments(arguments);
+        var nextThenable = then.apply(thenable, args);
+        return patchThenable(nextThenable);
+      };
+
+      var ocatch = thenable.catch;
+      thenable.catch = function () {
+        var args = Zone.bindArguments(arguments);
+        var nextThenable = ocatch.apply(thenable, args);
+        return patchThenable(nextThenable);
+      };
+      return thenable;
+    }
+  }
+}());
+
+
 Zone.patchableFn = function (obj, fnNames) {
   fnNames.forEach(function (name) {
     var delegate = obj[name];