Return a rejected promise instead of false on invalid model save

backbone.js

@@ -445,7 +445,7 @@
     // If the server returns an attributes hash that differs, the model's
     // state will be `set` again.
     save: function(key, val, options) {
-      var attrs, method, xhr, attributes = this.attributes;
+      var attrs, method, xhr, dfd = Backbone.Deferred(), attributes = this.attributes;
 
       // Handle both `"key", value` and `{key: value}` -style arguments.
       if (key == null || typeof key === 'object') {
@@ -461,9 +461,9 @@
       // `set(attr).save(null, opts)` with validation. Otherwise, check if
       // the model will be valid when the attributes, if any, are set.
       if (attrs && !options.wait) {
-        if (!this.set(attrs, options)) return false;
+        if (!this.set(attrs, options)) return dfd.reject();
       } else {
-        if (!this._validate(attrs, options)) return false;
+        if (!this._validate(attrs, options)) return dfd.reject();
       }
 
       // Set temporary attributes if `{wait: true}`.
@@ -519,7 +519,7 @@
 
       if (this.isNew()) {
         options.success();
-        return false;
+        return Backbone.Deferred().resolve();
       }
       wrapError(this, options);
 
@@ -1204,6 +1204,12 @@
     return Backbone.$.ajax.apply(Backbone.$, arguments);
   };
 
+  // Set the default promises library to proxy to `$`.
+  // Override this if you'd like to use a different library.
+  Backbone.Deferred = function() {
+    return Backbone.$.Deferred.apply(Backbone.$, arguments);
+  }
+
   // Backbone.Router
   // ---------------
 

test/model.js

@@ -489,7 +489,7 @@ $(document).ready(function() {
     ok(_.isEqual(this.syncArgs.model, doc));
 
     var newModel = new Backbone.Model;
-    equal(newModel.destroy(), false);
+    equal(newModel.destroy().state(), 'resolved');
   });
 
   test("non-persisted destroy", 1, function() {
@@ -959,18 +959,26 @@ $(document).ready(function() {
     var model = new Backbone.Model;
     model.validate = function(){ return 'invalid'; };
     model.sync = function(){ ok(false); };
-    strictEqual(model.save(), false);
+    model.save().then(function() {
+      ok(false);
+    }, function() {
+      ok(true);
+    });
   });
 
-  test("#1377 - Save without attrs triggers 'error'.", 1, function() {
+  test("#1377 - Save without attrs triggers 'error'.", 2, function() {
     var Model = Backbone.Model.extend({
       url: '/test/',
       sync: function(method, model, options){ options.success(); },
       validate: function(){ return 'invalid'; }
     });
     var model = new Model({id: 1});
     model.on('invalid', function(){ ok(true); });
-    model.save();
+    model.save().then(function() {
+      ok(false);
+    }, function() {
+      ok(true);
+    });
   });
 
   test("#1545 - `undefined` can be passed to a model constructor without coersion", function() {

test/sync.js

@@ -155,6 +155,21 @@ $(document).ready(function() {
     Backbone.sync('create', model);
   });
 
+  test("Backbone.Deferred", 2, function() {
+    Backbone.sync = function(settings){
+      return Backbone.Deferred().resolve();
+    };
+    var model = new Backbone.Model();
+    model.url = '/test';
+    model.validate = function(attrs) {
+      return !attrs.accept;
+    }
+    var result = model.save({accept: false});
+    strictEqual(result.state(), 'rejected');
+    result = model.save({accept: true});
+    strictEqual(result.state(), 'resolved');
+  });
+
   test("Call provided error callback on error.", 1, function() {
     var model = new Backbone.Model;
     model.url = '/test';