[es6] implement Object.assign

test/mjsunit/harmony/object-assign.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Based on Mozilla Array.of() tests at http://dxr.mozilla.org/mozilla-central/source/js/src/tests/ecma_6/Object/assign.js
+
+function checkDataProperty(object, propertyKey, value, writable, enumerable, configurable) {
+  var desc = Object.getOwnPropertyDescriptor(object, propertyKey);
+  assertFalse(desc === undefined);
+  assertTrue('value' in desc);
+  assertEquals(desc.value, value);
+  assertEquals(desc.writable, writable);
+  assertEquals(desc.enumerable, enumerable);
+  assertEquals(desc.configurable, configurable);
+}
+
+// 19.1.2.1 Object.assign ( target, ...sources )
+assertEquals(Object.assign.length, 2);
+
+// Basic functionality works with multiple sources
+(function basicMultipleSources() {
+  var a = {};
+  var b = { bProp: 1 };
+  var c = { cProp: 2 };
+  Object.assign(a, b, c);
+  assertEquals(a, {
+    bProp: 1,
+    cProp: 2
+  });
+})();
+
+// Basic functionality works with symbols
+// TODO: `b.aSymbol is not copied into a

[jsbell, 2014/09/08 17:22:42]

Extraneous (or missing) `

[caitp (gmail), 2014/09/08 17:48:27]

Acknowledged.

+/*(function basicSymbols() {
+  var a = {};
+  var b = { bProp: 1 };
+  var aSymbol = Symbol("aSymbol");
+  b[aSymbol] = 2;
+  Object.assign(a, b);
+  assertEquals(1, a.bProp);
+  assertEquals(2, a[aSymbol]);
+})();*/
+
+// Dies if target is null or undefined
+assertThrows(function() { return Object.assign(null, null); }, TypeError);
+assertThrows(function() { return Object.assign(null, {}); }, TypeError);
+assertThrows(function() { return Object.assign(undefined); }, TypeError);
+assertThrows(function() { return Object.assign(); }, TypeError);
+
+// Calls ToObject for target
+assertTrue(Object.assign(true, {}) instanceof Boolean);
+assertTrue(Object.assign(1, {}) instanceof Number);
+assertTrue(Object.assign("string", {}) instanceof String);
+var o = {};
+assertSame(Object.assign(o, {}), o);
+
+// Only [[Enumerable]] properties are assigned to target
+(function onlyEnumerablePropertiesAssigned() {
+  var source = Object.defineProperties({}, {
+    a: {value: 1, enumerable: true},
+    b: {value: 2, enumerable: false},
+  });
+  var target = Object.assign({}, source);
+  assertTrue("a" in target);
+  assertFalse("b" in target);
+})();
+
+// Properties are retrieved through Get()
+// Properties are assigned through Put()
+(function testPropertiesAssignedThroughPut() {
+  var setterCalled = false;
+  Object.assign({set a(v) { setterCalled = v }}, {a: true});
+  assertTrue(setterCalled);
+})();
+
+// Properties are retrieved through Get()
+// Properties are assigned through Put(): Existing property attributes are not altered
+(function propertiesAssignedExistingNotAltered() {
+  var source = {a: 1, b: 2, c: 3};
+  var target = {a: 0, b: 0, c: 0};
+  Object.defineProperty(target, "a", {enumerable: false});
+  Object.defineProperty(target, "b", {configurable: false});
+  Object.defineProperty(target, "c", {enumerable: false, configurable: false});
+  Object.assign(target, source);
+  checkDataProperty(target, "a", 1, true, false, true);
+  checkDataProperty(target, "b", 2, true, true, false);
+  checkDataProperty(target, "c", 3, true, false, false);
+})();
+
+// Properties are retrieved through Get()
+// Properties are assigned through Put(): Throws TypeError if non-writable
+(function propertiesAssignedTypeErrorNonWritable() {
+  var source = {a: 1};
+  var target = {a: 0};
+  Object.defineProperty(target, "a", {writable: false});
+  assertThrows(function() { return Object.assign(target, source); }, TypeError);
+  checkDataProperty(target, "a", 0, false, true, true);
+})();
+
+// Properties are retrieved through Get()
+// Put() creates standard properties; Property attributes from source are
+// ignored
+(function createsStandardProperties() {
+  var source = {a: 1, b: 2, c: 3, get d() { return 4 }};
+  Object.defineProperty(source, "b", {writable: false});
+  Object.defineProperty(source, "c", {configurable: false});
+  var target = Object.assign({}, source);
+  checkDataProperty(target, "a", 1, true, true, true);
+  checkDataProperty(target, "b", 2, true, true, true);
+  checkDataProperty(target, "c", 3, true, true, true);
+  checkDataProperty(target, "d", 4, true, true, true);
+})();
+
+// Properties created during traversal are not copied
+(function propertiesCreatedDuringTraversalNotCopied() {
+  var source = {get a() { this.b = 2 }};
+  var target = Object.assign({}, source);
+  assertTrue("a" in target);
+  assertFalse("b" in target);
+})();
+
+// String and Symbol valued properties are copied

[jsbell, 2014/09/08 17:22:42]

Add another TODO here for Symbol property?

[caitp (gmail), 2014/09/08 17:48:28]

All of the tests here were basically copy/pasted from the spidermonkey
Object.assign tests and adapted for mjsunit --- with the exception of tests
which make use of direct proxies (which is unfortunate, because they look very
useful here).

I believe this comment (which was pulled out of spidermonkey) is sort of a
misnomer, it should be "keyed" rather than "valued". There is a test (which is
commented out due to being broken) on line 33 which asserts that symbol keys are
copied.

It would probably make sense to move that test down here, or move this one up
there. I'll do that after investigating why it's not copying symbol keys.

+(function testStringAndSymbolPropertiesCopied() {
+  var keyA = "str-prop";
+  var source = {"str-prop": 1};
+  var target = Object.assign({}, source);
+  checkDataProperty(target, keyA, 1, true, true, true);
+})();
+
+// Intermediate exceptions do not stop property traversal, first exception is

[jsbell, 2014/09/08 17:22:42]

Add a property that *is* copied successfully, even if the rest throw?

[caitp (gmail), 2014/09/08 17:48:28]

asserting that log equals "ba" is asserting that both copies are copied (the
setter throws), even though the first setter threw an exception

+// reported (3)

[jsbell, 2014/09/08 17:22:42]

What's the '(3)' here?

[caitp (gmail), 2014/09/08 17:48:27]

These tests are pulled out of the spidermonkey Object.assign test suite, there
are a series of other tests here, which are numbered this way, but unfortunately
these all depend on direct proxies (we don't have a way of faking
[[OwnPropertyKeys]] in v8 currently).

This one sort of works around this using the assumption that the order of
properties in a literal will be the order that they appear in
[[OwnPropertyKeys]], which is spec-correct, but still not as robust as mocking
[[OwnPropertyKeys]] with a proxy.

Other tests using proxies were a bit harder to hack around the lack of direct
proxies and lack of support for 'ownKeys', but I'll look at adding more when I
have some time.

+(function testExceptionsDoNotStopFirstReported3() {
+  var ErrorA = function ErrorA() {};
+  var ErrorB = function ErrorB() {};
+  var log = "";
+  var source = { b: 1, a: 1 };
+  var target = {
+      set a(v) { log += "a"; throw new ErrorA },
+      set b(v) { log += "b"; throw new ErrorB },
+  };
+  assertThrows(function() { return Object.assign(target, source); }, ErrorB);
+  assertEquals(log, "ba");
+})();
+
+// TODO: Many of these tests depend on a more adequate Proxy implementation,
+// so that [[OwnPropertyKeys]] and other internal methods can be mocked. The
+// old-style Proxy implementation in v8 does not satisfy these needs.