Mojo JS bindings: introduce concepts that are more similar to C++ bindings:

mojo/edk/js/tests/binding_tests.js

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+define([
+    "gin/test/expect",
+    "mojo/public/js/bindings",
+    "mojo/public/interfaces/bindings/tests/math_calculator.mojom",
+    "mojo/public/js/threading",
+    "gc",
+], function(expect,
+            bindings,
+            math,
+            threading,
+            gc) {
+  testIsBound()
+      .then(testReusable)
+      .then(function() {
+    this.result = "PASS";
+    gc.collectGarbage();  // should not crash
+    threading.quit();
+  }.bind(this)).catch(function(e) {
+    this.result = "FAIL: " + (e.stack || e);
+    threading.quit();
+  }.bind(this));
+
+  function CalculatorImpl() {
+    this.total = 0;
+  }
+
+  CalculatorImpl.prototype.clear = function() {
+    this.total = 0;
+    return Promise.resolve({value: this.total});
+  };
+
+  CalculatorImpl.prototype.add = function(value) {
+    this.total += value;
+    return Promise.resolve({value: this.total});
+  };
+
+  CalculatorImpl.prototype.multiply = function(value) {
+    this.total *= value;
+    return Promise.resolve({value: this.total});
+  };
+
+  function testIsBound() {
+    var binding = new bindings.Binding(math.Calculator, new CalculatorImpl());
+    expect(binding.isBound()).toBeFalsy();
+
+    var calc = new math.CalculatorPtr();
+    var request = bindings.makeRequest(calc);
+    binding.bind(request);
+    expect(binding.isBound()).toBeTruthy();
+
+    binding.close();
+    expect(binding.isBound()).toBeFalsy();
+
+    return Promise.resolve();
+  }
+
+  function testReusable() {
+    var calc1 = new math.CalculatorPtr();
+    var calc2 = new math.CalculatorPtr();
+
+    var calcBinding = new bindings.Binding(math.Calculator,
+                                           new CalculatorImpl(),
+                                           bindings.makeRequest(calc1));
+
+    var promise = calc1.add(2).then(function(response) {
+      expect(response.value).toBe(2);
+      calcBinding.bind(bindings.makeRequest(calc2));
+      return calc2.add(2);
+    }).then(function(response) {
+      expect(response.value).toBe(4);
+      return Promise.resolve();
+    });
+
+    return promise;
+  }
+});