Date.protoype.toJSON should look for toISOString once (#3996)

The toJSON method should be searched on the `this` object
only once. In case of normal objects there were no problems
however when a Proxy object is used as the `this` argument
for the Date.prototype.toJSON method the Proxy's `get` method
was invoked twice.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com

tests/jerry/date-tojson.js

@@ -0,0 +1,22 @@
+// 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.
+
+var obj = {
+    toISOString: function() { return "RESULT-ToISOString"; },
+    valueOf: function() { return "RESULT-valueOf"; }
+};
+
+var result = Date.prototype.toJSON.call(obj);
+
+assert(result === "RESULT-ToISOString");

tests/jerry/es.next/proxy-date-prototype-json.js

@@ -0,0 +1,45 @@
+// 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 the Date.prototype.toJSON method's internal operation order
+ * by creating a Proxy to catch the method invokations.
+ */
+var found = [];
+
+var target = {
+  toString: function() { return "TARGET_toString"; },
+  toISOString: function() { return "TARGET_toISOString"; }
+};
+
+var prox = new Proxy(target, {
+  get: function(trg, key) {
+    found.push(key);
+    return trg[key];
+  }
+});
+
+/* Date.prototype.toJSON -> ... -> <target>.toISOString() */
+var json_result = Date.prototype.toJSON.call(prox);
+assert(json_result === "TARGET_toISOString");
+
+/* Data.prototype.toJSON -> toPrimitive -> Get -> [[Get]]
+ * The first element in the "found" properties should be the "@@toPrimitive" well-known Symbol.
+ */
+assert(found[0] === Symbol.toPrimitive);
+
+/* Date.prototype.toJSON -> Invoke -> GetMethod -> GetV -> [[Get]]
+ * All other elements are "methods" and there should be no duplicates.
+ */
+var methods = found.slice(1);
+assert(methods.toString() === "valueOf,toString,toISOString");