Implement Promise.prototype.onFinally (#3987)

The algorith is based on ECMA-262 v11, 25.6.5.3

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

tests/jerry/es.next/promise-on-finally.js

@@ -0,0 +1,145 @@
+/* Copyright JS Foundation and other contributors, http://js.foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// test basic functionality
+var order = [];
+var reason = {};
+var reject = Promise.reject(reason);
+reject.then = function() {
+  order.push(1);
+  return Promise.prototype.then.apply(this, arguments);
+};
+
+var value = {};
+var resolve = Promise.resolve(value);
+resolve.then = function() {
+  order.push(4);
+  return Promise.prototype.then.apply(this, arguments);
+};
+
+reject.catch(function(e) {
+	order.push(2);
+	throw e;
+}).finally(function() {
+	order.push(3);
+	return resolve;
+}).catch(function(e) {
+	order.push(5);
+});
+
+function __checkAsync() {
+  assert(order.length === 5);
+  for (var i = 0; i < order.length; i++)
+  {
+    assert(i + 1 === order[i]);
+  }
+}
+
+// check length property
+var desc = Object.getOwnPropertyDescriptor(Promise.prototype.finally, "length");
+assert(desc.value === 1);
+assert(desc.enumerable === false);
+assert(desc.configurable === true);
+assert(desc.writable === false);
+
+// invokes then with function
+var target = new Promise(function() {});
+var returnValue = {};
+var callCount = 0;
+var thisValue = null;
+var argCount = null;
+var firstArg = null;
+var secondArg = null;
+
+target.then = function(a, b) {
+  callCount += 1;
+
+  thisValue = this;
+  argCount = arguments.length;
+  firstArg = a;
+  secondArg = b;
+
+  return returnValue;
+};
+
+var originalFinallyHandler = function() {};
+var result = Promise.prototype.finally.call(target, originalFinallyHandler, 2, 3);
+
+(callCount === 1);
+assert(thisValue === target);
+assert(argCount === 2);
+assert(typeof firstArg === 'function');
+assert(firstArg.length === 1);
+assert(typeof secondArg === 'function');
+assert(secondArg.length === 1);
+assert(result === returnValue);
+
+// invokes then with non-function
+result = Promise.prototype.finally.call(target, 1, 2, 3);
+
+assert(callCount === 2);
+assert(thisValue === target);
+assert(argCount === 2);
+assert(firstArg === 1);
+assert(secondArg === 1);
+assert(result == returnValue);
+
+// thes when 'then' is not callable
+var thrower = function() {
+  throw 42;
+};
+
+var symbol = Symbol();
+var p = new Promise(function() {});
+
+p.then = undefined;
+try {
+  Promise.prototype.finally.call(p, thrower);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+p.then = null;
+try {
+  Promise.prototype.finally.call(p, thrower);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+p.then = 1;
+try {
+  Promise.prototype.finally.call(p, thrower);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+p.then = symbol;
+try {
+  Promise.prototype.finally.call(p, thrower);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+p.then = {};
+try {
+  Promise.prototype.finally.call(p, thrower);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}