diff --git a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/AbstractNode.java b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/AbstractNode.java
index fb99016a30b..b2961fd793a 100644
--- a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/AbstractNode.java
+++ b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/AbstractNode.java
@@ -16,16 +16,30 @@
 
 package org.jetbrains.kotlin.js.backend.ast;
 
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.js.backend.JsToStringGenerationVisitor;
 import org.jetbrains.kotlin.js.backend.ast.metadata.HasMetadata;
+import org.jetbrains.kotlin.js.backend.ast.metadata.HasMetadataImpl;
 import org.jetbrains.kotlin.js.util.TextOutputImpl;
 
-import java.util.LinkedList;
+import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
-abstract class AbstractNode extends HasMetadata implements JsNode {
-    private List<JsComment> commentsBefore = null;
-    private List<JsComment> commentsAfter = null;
+abstract class AbstractNode implements JsNode, HasMetadata {
+    private static class Internals extends HasMetadataImpl {
+        List<JsComment> commentsBefore = null;
+        List<JsComment> commentsAfter = null;
+    }
+
+    private Internals internals = null;
+
+    private Internals getInternals() {
+        if (internals == null) {
+            internals = new Internals();
+        }
+        return internals;
+    }
 
     @Override
     public String toString() {
@@ -48,21 +62,56 @@ abstract class AbstractNode extends HasMetadata implements JsNode {
 
     @Override
     public List<JsComment> getCommentsBeforeNode() {
-        return commentsBefore;
+        return internals == null ? null : internals.commentsBefore;
     }
 
     @Override
     public List<JsComment> getCommentsAfterNode() {
-        return commentsAfter;
+        return internals == null ? null : internals.commentsAfter;
     }
 
     @Override
     public void setCommentsBeforeNode(List<JsComment> comments) {
-        commentsBefore = comments;
+        getInternals().commentsBefore = comments;
     }
 
     @Override
     public void setCommentsAfterNode(List<JsComment> comments) {
-        commentsAfter = comments;
+        getInternals().commentsAfter = comments;
+    }
+
+    @Override
+    public <T> T getData(@NotNull String key) {
+        return getInternals().getData(key);
+    }
+
+    @Override
+    public <T> void setData(@NotNull String key, T value) {
+        getInternals().setData(key, value);
+    }
+
+    @Override
+    public boolean hasData(@NotNull String key) {
+        return internals != null && internals.hasData(key);
+    }
+
+    @Override
+    public void removeData(@NotNull String key) {
+        if (internals != null) {
+            internals.removeData(key);
+        }
+    }
+
+    @Override
+    public void copyMetadataFrom(@NotNull HasMetadata other) {
+        if (!other.getRawMetadata().isEmpty()) {
+            getInternals().copyMetadataFrom(other);
+        }
+    }
+
+    @NotNull
+    @Override
+    public Map<String, Object> getRawMetadata() {
+        return internals != null ? internals.getRawMetadata() : Collections.emptyMap();
     }
 }
diff --git a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsName.java b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsName.java
index 3c4cf7b8052..bee0fff2dfd 100644
--- a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsName.java
+++ b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsName.java
@@ -5,13 +5,13 @@
 package org.jetbrains.kotlin.js.backend.ast;
 
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.kotlin.js.backend.ast.metadata.HasMetadata;
+import org.jetbrains.kotlin.js.backend.ast.metadata.HasMetadataImpl;
 import org.jetbrains.kotlin.js.common.Symbol;
 
 /**
  * An abstract base class for named JavaScript objects.
  */
-public class JsName extends HasMetadata implements Symbol {
+public class JsName extends HasMetadataImpl implements Symbol {
   @NotNull
   private final String ident;
 
diff --git a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/metadata/HasMetadata.kt b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/metadata/HasMetadata.kt
index f9c5ab23262..f89b453aa37 100644
--- a/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/metadata/HasMetadata.kt
+++ b/js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/metadata/HasMetadata.kt
@@ -16,27 +16,45 @@
 
 package org.jetbrains.kotlin.js.backend.ast.metadata
 
-abstract class HasMetadata {
-    private val metadata: MutableMap<String, Any?> = hashMapOf()
+interface HasMetadata {
+    fun <T> getData(key: String): T
+    fun <T> setData(key: String, value: T)
+    fun hasData(key: String): Boolean
+    fun removeData(key: String)
+    fun copyMetadataFrom(other: HasMetadata)
+    fun getRawMetadata(): Map<String, Any?>
+}
 
-    fun <T> getData(key: String): T {
-        @Suppress("UNCHECKED_CAST")
-        return metadata[key] as T
+open class HasMetadataImpl : HasMetadata {
+    private var metadataImpl: MutableMap<String, Any?>? = null
+
+    private val metadata: MutableMap<String, Any?>
+        get() = metadataImpl ?: hashMapOf<String, Any?>().also { metadataImpl = it }
+
+    final override fun <T> getData(key: String): T {
+        @Suppress("UNCHECKED_CAST") return metadata[key] as T
     }
 
-    fun <T> setData(key: String, value: T) {
+    final override fun <T> setData(key: String, value: T) {
         metadata[key] = value
     }
 
-    fun hasData(key: String): Boolean {
-        return metadata.containsKey(key)
+    final override fun hasData(key: String): Boolean {
+        return metadataImpl?.containsKey(key) == true
     }
 
-    fun removeData(key: String) {
-        metadata.remove(key)
+    final override fun removeData(key: String) {
+        metadataImpl?.remove(key)
     }
 
-    fun copyMetadataFrom(other: HasMetadata) {
-        metadata.putAll(other.metadata)
+    final override fun copyMetadataFrom(other: HasMetadata) {
+        val otherRawMetadata = other.getRawMetadata()
+        if (otherRawMetadata.isNotEmpty()) {
+            metadata.putAll(otherRawMetadata)
+        }
+    }
+
+    final override fun getRawMetadata(): Map<String, Any?> {
+        return metadataImpl ?: emptyMap()
     }
 }