Optional Chaining Operator ?.

rhino/src/main/java/org/mozilla/javascript/CodeGenerator.java

@@ -602,6 +602,7 @@ private void visitExpression(Node node, int contextFlags) {
 
             case Token.REF_CALL:
             case Token.CALL:
+            case Token.CALL_OPTIONAL:
             case Token.NEW:
                 {
                     if (type == Token.NEW) {
@@ -686,6 +687,11 @@ private void visitExpression(Node node, int contextFlags) {
                     resolveForwardGoto(afterElseJumpStart);
                 }
                 break;
+            case Token.GETPROP_OPTIONAL:
+                visitExpression(child, 0);
+                child = child.getNext();
+                addStringOp(type, child.getString());
+                break;
 
             case Token.GETPROP:
             case Token.GETPROPNOWARN:
@@ -962,6 +968,7 @@ private void visitExpression(Node node, int contextFlags) {
                 visitArrayComprehension(node, child, child.getNext());
                 break;
 
+            case Token.REF_SPECIAL_OPTIONAL:
             case Token.REF_SPECIAL:
                 visitExpression(child, 0);
                 addStringOp(type, (String) node.getProp(Node.NAME_PROP));
@@ -1057,6 +1064,7 @@ private void generateCallFunAndThis(Node left) {
                     stackChange(2);
                     break;
                 }
+            case Token.GETPROP_OPTIONAL:
             case Token.GETPROP:
             case Token.GETELEM:
                 {
@@ -1068,6 +1076,11 @@ private void generateCallFunAndThis(Node left) {
                         // stack: ... target -> ... function thisObj
                         addStringOp(Icode_PROP_AND_THIS, property);
                         stackChange(1);
+                    } else if (type == Token.GETPROP_OPTIONAL) {
+                        String property = id.getString();
+                        // stack: ... target -> ... function thisObj
+                        addStringOp(Icode_PROP_AND_THIS_OPTIONAL, property);
+                        stackChange(1);
                     } else {
                         visitExpression(id, 0);
                         // stack: ... target id -> ... function thisObj

rhino/src/main/java/org/mozilla/javascript/IRFactory.java

@@ -141,6 +141,7 @@ private Node transform(AstNode node) {
                 return transformBlock(node);
             case Token.BREAK:
                 return transformBreak((BreakStatement) node);
+            case Token.CALL_OPTIONAL:
             case Token.CALL:
                 return transformFunctionCall((FunctionCall) node);
             case Token.CONTINUE:
@@ -161,6 +162,7 @@ private Node transform(AstNode node) {
                 return transformGenExpr((GeneratorExpression) node);
             case Token.GETELEM:
                 return transformElementGet((ElementGet) node);
+            case Token.QUESTION_DOT:
             case Token.GETPROP:
                 return transformPropertyGet((PropertyGet) node);
             case Token.HOOK:
@@ -347,7 +349,8 @@ private Node arrayCompTransformHelper(ArrayComprehension node, String arrayName)
         Node call =
                 createCallOrNew(
                         Token.CALL,
-                        createPropertyGet(parser.createName(arrayName), null, "push", 0));
+                        createPropertyGet(
+                                parser.createName(arrayName), null, "push", 0, node.type));
 
         Node body = new Node(Token.EXPR_VOID, call, lineno);
 
@@ -603,7 +606,10 @@ private Node transformFunction(FunctionNode fn) {
     }
 
     private Node transformFunctionCall(FunctionCall node) {
-        Node call = createCallOrNew(Token.CALL, transform(node.getTarget()));
+        Node call =
+                createCallOrNew(
+                        node.type == Token.CALL_OPTIONAL ? Token.CALL_OPTIONAL : Token.CALL,
+                        transform(node.getTarget()));
         call.setLineno(node.getLineno());
         List<AstNode> args = node.getArguments();
         for (int i = 0; i < args.size(); i++) {
@@ -917,7 +923,7 @@ private Node transformComputedPropertyKey(ComputedPropertyKey node) {
     private Node transformPropertyGet(PropertyGet node) {
         Node target = transform(node.getTarget());
         String name = node.getProperty().getIdentifier();
-        return createPropertyGet(target, null, name, 0);
+        return createPropertyGet(target, null, name, 0, node.type);
     }
 
     private Node transformTemplateLiteral(TemplateLiteral node) {
@@ -1239,7 +1245,7 @@ private Node transformXmlRef(Node pn, XmlRef node, int memberTypeFlags) {
         String ns = namespace != null ? namespace.getIdentifier() : null;
         if (node instanceof XmlPropRef) {
             String name = ((XmlPropRef) node).getPropName().getIdentifier();
-            return createPropertyGet(pn, ns, name, memberTypeFlags);
+            return createPropertyGet(pn, ns, name, memberTypeFlags, node.type);
         }
         Node expr = transform(((XmlElemRef) node).getExpression());
         return createElementGet(pn, ns, expr, memberTypeFlags);
@@ -1875,18 +1881,27 @@ private static Node createIncDec(int nodeType, boolean post, Node child) {
     }
 
     private Node createPropertyGet(
-            Node target, String namespace, String name, int memberTypeFlags) {
+            Node target, String namespace, String name, int memberTypeFlags, int type) {
         if (namespace == null && memberTypeFlags == 0) {
             if (target == null) {
                 return parser.createName(name);
             }
             parser.checkActivationName(name, Token.GETPROP);
             if (ScriptRuntime.isSpecialProperty(name)) {
-                Node ref = new Node(Token.REF_SPECIAL, target);
+                Node ref =
+                        new Node(
+                                type == Token.QUESTION_DOT
+                                        ? Token.REF_SPECIAL_OPTIONAL
+                                        : Token.REF_SPECIAL,
+                                target);
                 ref.putProp(Node.NAME_PROP, name);
                 return new Node(Token.GET_REF, ref);
             }
-            return new Node(Token.GETPROP, target, Node.newString(name));
+
+            return new Node(
+                    type == Token.QUESTION_DOT ? Token.GETPROP_OPTIONAL : Token.GETPROP,
+                    target,
+                    Node.newString(name));
         }
         Node elem = Node.newString(name);
         memberTypeFlags |= Node.PROPERTY_FLAG;

rhino/src/main/java/org/mozilla/javascript/Icode.java

@@ -142,9 +142,9 @@ abstract class Icode {
             Icode_TEMPLATE_LITERAL_CALLSITE = -74,
             Icode_LITERAL_KEYS = -75,
             Icode_LITERAL_KEY_SET = -76,
-
+            Icode_PROP_AND_THIS_OPTIONAL = -77,
             // Last icode
-            MIN_ICODE = -76;
+            MIN_ICODE = -77;
 
     static String bytecodeName(int bytecode) {
         if (!validBytecode(bytecode)) {
@@ -190,6 +190,8 @@ static String bytecodeName(int bytecode) {
                 return "NAME_AND_THIS";
             case Icode_PROP_AND_THIS:
                 return "PROP_AND_THIS";
+            case Icode_PROP_AND_THIS_OPTIONAL:
+                return "PROP_AND_THIS_OPTIONAL";
             case Icode_ELEM_AND_THIS:
                 return "ELEM_AND_THIS";
             case Icode_VALUE_AND_THIS:

rhino/src/main/java/org/mozilla/javascript/Interpreter.java

@@ -1598,6 +1598,16 @@ private static Object interpretLoop(Context cx, CallFrame frame, Object throwabl
                                                     lhs, stringReg, cx, frame.scope);
                                     continue Loop;
                                 }
+                            case Token.GETPROP_OPTIONAL:
+                                {
+                                    Object lhs = stack[stackTop];
+                                    if (lhs == DBL_MRK)
+                                        lhs = ScriptRuntime.wrapNumber(sDbl[stackTop]);
+                                    stack[stackTop] =
+                                            ScriptRuntime.getObjectPropOptional(
+                                                    lhs, stringReg, cx, frame.scope);
+                                    continue Loop;
+                                }
                             case Token.SETPROP:
                                 {
                                     Object rhs = stack[stackTop];
@@ -1694,6 +1704,19 @@ private static Object interpretLoop(Context cx, CallFrame frame, Object throwabl
                                 ++stackTop;
                                 stack[stackTop] = ScriptRuntime.lastStoredScriptable(cx);
                                 continue Loop;
+                            case Icode_PROP_AND_THIS_OPTIONAL:
+                                {
+                                    Object obj = stack[stackTop];
+                                    if (obj == DBL_MRK)
+                                        obj = ScriptRuntime.wrapNumber(sDbl[stackTop]);
+                                    // stringReg: property
+                                    stack[stackTop] =
+                                            ScriptRuntime.getPropFunctionAndThisOptional(
+                                                    obj, stringReg, cx, frame.scope);
+                                    ++stackTop;
+                                    stack[stackTop] = ScriptRuntime.lastStoredScriptable(cx);
+                                    continue Loop;
+                                }
                             case Icode_PROP_AND_THIS:
                                 {
                                     Object obj = stack[stackTop];
@@ -1744,6 +1767,7 @@ private static Object interpretLoop(Context cx, CallFrame frame, Object throwabl
                                     continue Loop;
                                 }
                             case Token.CALL:
+                            case Token.CALL_OPTIONAL:
                             case Icode_TAIL_CALL:
                             case Token.REF_CALL:
                                 {
@@ -2260,6 +2284,17 @@ private static Object interpretLoop(Context cx, CallFrame frame, Object throwabl
                                                     obj, stringReg, cx, frame.scope);
                                     continue Loop;
                                 }
+                            case Token.REF_SPECIAL_OPTIONAL:
+                                {
+                                    // stringReg: name of special property
+                                    Object obj = stack[stackTop];
+                                    if (obj == DBL_MRK)
+                                        obj = ScriptRuntime.wrapNumber(sDbl[stackTop]);
+                                    stack[stackTop] =
+                                            ScriptRuntime.optionalSpecialRef(
+                                                    obj, stringReg, cx, frame.scope);
+                                    continue Loop;
+                                }
                             case Token.REF_MEMBER:
                                 {
                                     // indexReg: flags

rhino/src/main/java/org/mozilla/javascript/Parser.java

@@ -2795,6 +2795,7 @@ private AstNode memberExprTail(boolean allowCallSyntax, AstNode pn) throws IOExc
             int tt = peekToken();
             switch (tt) {
                 case Token.DOT:
+                case Token.QUESTION_DOT:
                 case Token.DOTDOT:
                     lineno = ts.lineno;
                     pn = propertyAccess(tt, pn);
@@ -2924,8 +2925,28 @@ private AstNode propertyAccess(int tt, AstNode pn) throws IOException {
         }
 
         AstNode ref = null; // right side of . or .. operator
-
         int token = nextToken();
+        if (token == Token.LP && tt == Token.QUESTION_DOT) {
+            // optional chaining operator method call, o.func?.()
+            var pos = pn.getPosition();
+            pn.setType(Token.QUESTION_DOT);
+            consumeToken();
+            checkCallRequiresActivation(pn);
+            FunctionCall f = new FunctionCall(pos);
+            f.setTarget(pn);
+            // Assign the line number for the function call to where
+            // the paren appeared, not where the name expression started.
+            f.setLineno(lineno);
+            f.setLp(ts.tokenBeg - pos);
+            List<AstNode> args = argumentList();
+            if (args != null && args.size() > ARGC_LIMIT) reportError("msg.too.many.function.args");
+            f.setArguments(args);
+            f.setRp(ts.tokenBeg - pos);
+            f.setLength(ts.tokenEnd - pos);
+            f.setType(Token.CALL_OPTIONAL);
+            return f;
+        }
+
         switch (token) {
             case Token.THROW:
                 // needed for generator.throw();
@@ -2957,7 +2978,6 @@ private AstNode propertyAccess(int tt, AstNode pn) throws IOException {
                     ref = propertyName(-1, memberTypeFlags);
                     break;
                 }
-
             default:
                 if (compilerEnv.isReservedKeywordAsIdentifier()) {
                     // allow keywords as property names, e.g. ({if: 1})
@@ -2982,9 +3002,20 @@ private AstNode propertyAccess(int tt, AstNode pn) throws IOException {
         result.setLineno(pn.getLineno());
         result.setLeft(pn); // do this after setting position
         result.setRight(ref);
+
+        if (tt == Token.QUESTION_DOT && result instanceof PropertyGet) {
+            result.setType(Token.QUESTION_DOT);
+        }
         return result;
     }
 
+    private static AstNode cloneNode(AstNode target) {
+        var newParser = new Parser();
+        var root = newParser.parse(target.toSource(), "", 1);
+        var targetCopy = ((ExpressionStatement) root.first).getExpression();
+        return targetCopy;
+    }
+
     /**
      * Xml attribute expression:
      *

rhino/src/main/java/org/mozilla/javascript/ScriptRuntime.java

@@ -1739,6 +1739,22 @@ public static Object getObjectProp(Object obj, String property, Context cx, Scri
         return getObjectProp(sobj, property, cx);
     }
 
+    public static Object getObjectPropOptional(
+            Object obj, String property, Context cx, Scriptable scope) {
+        if (obj == null || Undefined.isUndefined(obj)) {
+            return Undefined.instance;
+        }
+        return getObjectProp(obj, property, cx, scope);
+    }
+
+    public static Object getObjectPropOptional(
+            Scriptable obj, String property, Context cx, Scriptable scope) {
+        if (obj == null || Undefined.isUndefined(obj)) {
+            return Undefined.instance;
+        }
+        return getObjectProp(obj, property, cx);
+    }
+
     public static Object getObjectProp(Scriptable obj, String property, Context cx) {
 
         Object result = ScriptableObject.getProperty(obj, property);
@@ -1971,6 +1987,11 @@ public static Ref specialRef(Object obj, String specialProperty, Context cx, Scr
         return SpecialRef.createSpecial(cx, scope, obj, specialProperty);
     }
 
+    public static Ref optionalSpecialRef(
+            Object obj, String specialProperty, Context cx, Scriptable scope) {
+        return SpecialOptionalRef.create(cx, scope, obj, specialProperty);
+    }
+
     /** @deprecated Use {@link #delete(Object, Object, Context, Scriptable, boolean)} instead */
     @Deprecated
     public static Object delete(Object obj, Object id, Context cx) {
@@ -2617,6 +2638,20 @@ public static Callable getElemFunctionAndThis(
         return (Callable) value;
     }
 
+    public static Callable getPropFunctionAndThisOptional(
+            Object obj, String property, Context cx, Scriptable scope) {
+
+        Scriptable thisObj = toObjectOrNull(cx, obj, scope);
+        if (thisObj == null) {
+            throw undefCallError(obj, property);
+        }
+
+        Object value = ScriptableObject.getProperty(thisObj, property);
+        if (Scriptable.NOT_FOUND == value || Undefined.isUndefined(value) || value == null)
+            return (cx1, scope1, thisObj2, args) -> Undefined.instance;
+        return getPropFunctionAndThisHelper(obj, property, cx, thisObj);
+    }
+
     /**
      * Prepare for calling obj.property(...): return function corresponding to obj.property and make
      * obj properly converted to Scriptable available as ScriptRuntime.lastStoredScriptable() for

rhino/src/main/java/org/mozilla/javascript/SpecialOptionalRef.java

@@ -0,0 +1,29 @@
+package org.mozilla.javascript;
+
+class SpecialOptionalRef extends Ref {
+    Ref specialRef;
+
+    private SpecialOptionalRef(Ref specialRef) {
+        this.specialRef = specialRef;
+    }
+
+    public static Ref create(Context cx, Scriptable scope, Object object, String name) {
+        Scriptable target = ScriptRuntime.toObjectOrNull(cx, object, scope);
+        if (target != null && target != Undefined.instance) {
+            return new SpecialOptionalRef(SpecialRef.createSpecial(cx, scope, object, name));
+        }
+        return new SpecialOptionalRef(null);
+    }
+
+    @Override
+    public Object get(Context cx) {
+        if (specialRef == null) return Undefined.instance;
+        return specialRef.get(cx);
+    }
+
+    @Deprecated
+    @Override
+    public Object set(Context cx, Object value) {
+        throw new IllegalStateException();
+    }
+}