diff --git a/jso/apis/src/main/java/org/teavm/jso/core/JSPromise.java b/jso/apis/src/main/java/org/teavm/jso/core/JSPromise.java
index a4f2ba00e..dbc87e642 100644
--- a/jso/apis/src/main/java/org/teavm/jso/core/JSPromise.java
+++ b/jso/apis/src/main/java/org/teavm/jso/core/JSPromise.java
@@ -22,9 +22,9 @@ import org.teavm.jso.JSFunctor;
 import org.teavm.jso.JSMethod;
 import org.teavm.jso.JSObject;
 import org.teavm.jso.JSProperty;
-import org.teavm.jso.util.function.JSConsumer;
-import org.teavm.jso.util.function.JSFunction;
-import org.teavm.jso.util.function.JSSupplier;
+import org.teavm.jso.function.JSConsumer;
+import org.teavm.jso.function.JSMapping;
+import org.teavm.jso.function.JSSupplier;
 
 /**
  * Interface for interacting with JavaScript
@@ -76,29 +76,29 @@ public class JSPromise<T> implements JSObject {
     public static native <V> JSPromise<V> reject(Object reason);
 
     /** Call {@code onFulfilled} with the success value, resolving with its return value. */
-    public native <V> JSPromise<V> then(JSFunction<T, V> onFulfilled);
+    public native <V> JSPromise<V> then(JSMapping<T, V> onFulfilled);
 
     /** Call {@code onFulfilled} with the success value or {@code onRejected} with the reject reason,
      *  resolving with its return value. */
-    public native <V> JSPromise<V> then(JSFunction<T, V> onFulfilled, JSFunction<Object, V> onRejected);
+    public native <V> JSPromise<V> then(JSMapping<T, V> onFulfilled, JSMapping<Object, V> onRejected);
 
     /** Call {@code onFulfilled} with the success value, returning a new promise. */
     @JSMethod("then")
-    public native <V> JSPromise<V> flatThen(JSFunction<T, ? extends JSPromise<V>> onFulfilled);
+    public native <V> JSPromise<V> flatThen(JSMapping<T, ? extends JSPromise<V>> onFulfilled);
 
     /** Call {@code onFulfilled} with the success value or {@code onRejected} with the reject reason,
      *  returning a new promise. */
     @JSMethod("then")
-    public native <V> JSPromise<V> flatThen(JSFunction<T, ? extends JSPromise<V>> onFulfilled,
-                                              JSFunction<Object, ? extends JSPromise<V>> onRejected);
+    public native <V> JSPromise<V> flatThen(JSMapping<T, ? extends JSPromise<V>> onFulfilled,
+                                              JSMapping<Object, ? extends JSPromise<V>> onRejected);
 
     /** Call {@code onRejected} with the reject reason, resolving with its return value. */
     @JSMethod("catch")
-    public native <V> JSPromise<V> catchError(JSFunction<Object, V> onRejected);
+    public native <V> JSPromise<V> catchError(JSMapping<Object, V> onRejected);
 
     /** Call {@code onRejected} with the reject reason, returning a new promise. */
     @JSMethod("catch")
-    public native <V> JSPromise<V> flatCatchError(JSFunction<Object, ? extends JSPromise<V>> onRejected);
+    public native <V> JSPromise<V> flatCatchError(JSMapping<Object, ? extends JSPromise<V>> onRejected);
 
     /** Call {@code onFinally} after settling, ignoring the return value. */
     @JSMethod("finally")
diff --git a/jso/apis/src/main/java/org/teavm/jso/util/function/JSConsumer.java b/jso/apis/src/main/java/org/teavm/jso/function/JSConsumer.java
similarity index 93%
rename from jso/apis/src/main/java/org/teavm/jso/util/function/JSConsumer.java
rename to jso/apis/src/main/java/org/teavm/jso/function/JSConsumer.java
index b4b2b1b1f..dcf62c0b6 100644
--- a/jso/apis/src/main/java/org/teavm/jso/util/function/JSConsumer.java
+++ b/jso/apis/src/main/java/org/teavm/jso/function/JSConsumer.java
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2023 Bernd Busse.
+ *  Copyright 2024 Alexey Andreev.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.util.function;
+package org.teavm.jso.function;
 
 import java.util.Objects;
 import org.teavm.jso.JSFunctor;
diff --git a/jso/apis/src/main/java/org/teavm/jso/util/function/JSFunction.java b/jso/apis/src/main/java/org/teavm/jso/function/JSMapping.java
similarity index 76%
rename from jso/apis/src/main/java/org/teavm/jso/util/function/JSFunction.java
rename to jso/apis/src/main/java/org/teavm/jso/function/JSMapping.java
index 8e9c410ec..8667243d6 100644
--- a/jso/apis/src/main/java/org/teavm/jso/util/function/JSFunction.java
+++ b/jso/apis/src/main/java/org/teavm/jso/function/JSMapping.java
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2023 Bernd Busse.
+ *  Copyright 2024 Alexey Andreev.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.util.function;
+package org.teavm.jso.function;
 
 import java.util.Objects;
 import org.teavm.jso.JSFunctor;
@@ -21,10 +21,10 @@ import org.teavm.jso.JSObject;
 
 @FunctionalInterface
 @JSFunctor
-public interface JSFunction<T, R> extends JSObject {
+public interface JSMapping<T, R> extends JSObject {
     R apply(T t);
 
-    default <V> JSFunction<T, V> andThen(JSFunction<? super R, ? extends V> after) {
+    default <V> JSMapping<T, V> andThen(JSMapping<? super R, ? extends V> after) {
         Objects.requireNonNull(after);
 
         return (T t) -> {
@@ -33,7 +33,7 @@ public interface JSFunction<T, R> extends JSObject {
         };
     }
 
-    default <V> JSFunction<V, R> compose(JSFunction<? super V, ? extends T> before) {
+    default <V> JSMapping<V, R> compose(JSMapping<? super V, ? extends T> before) {
         Objects.requireNonNull(before);
 
         return (V v) -> {
@@ -42,7 +42,7 @@ public interface JSFunction<T, R> extends JSObject {
         };
     }
 
-    static <T> JSFunction<T, T> identity() {
+    static <T> JSMapping<T, T> identity() {
         return (T t) -> {
             return t;
         };
diff --git a/jso/apis/src/main/java/org/teavm/jso/util/function/JSSupplier.java b/jso/apis/src/main/java/org/teavm/jso/function/JSSupplier.java
similarity index 91%
rename from jso/apis/src/main/java/org/teavm/jso/util/function/JSSupplier.java
rename to jso/apis/src/main/java/org/teavm/jso/function/JSSupplier.java
index 31caef3d3..6670906f2 100644
--- a/jso/apis/src/main/java/org/teavm/jso/util/function/JSSupplier.java
+++ b/jso/apis/src/main/java/org/teavm/jso/function/JSSupplier.java
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2023 Bernd Busse.
+ *  Copyright 2024 Alexey Andreev.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.util.function;
+package org.teavm.jso.function;
 
 import org.teavm.jso.JSFunctor;
 import org.teavm.jso.JSObject;
diff --git a/samples/promise/src/main/java/org/teavm/samples/promise/PromiseExample.java b/samples/promise/src/main/java/org/teavm/samples/promise/PromiseExample.java
index cd2aa9834..812558bb6 100644
--- a/samples/promise/src/main/java/org/teavm/samples/promise/PromiseExample.java
+++ b/samples/promise/src/main/java/org/teavm/samples/promise/PromiseExample.java
@@ -21,9 +21,9 @@ import org.teavm.jso.browser.Window;
 import org.teavm.jso.core.JSArray;
 import org.teavm.jso.core.JSPromise;
 import org.teavm.jso.core.JSString;
-import org.teavm.jso.util.function.JSConsumer;
-import org.teavm.jso.util.function.JSFunction;
-import org.teavm.jso.util.function.JSSupplier;
+import org.teavm.jso.function.JSConsumer;
+import org.teavm.jso.function.JSMapping;
+import org.teavm.jso.function.JSSupplier;
 
 public final class PromiseExample {
     private static long start = System.currentTimeMillis();
@@ -67,15 +67,15 @@ public final class PromiseExample {
     private static void checkFunctionalInterface() {
         JSSupplier<Integer> supplier = () -> 23;
 
-        JSFunction<Integer, Integer> addTwenty = value -> value + 20;
-        JSFunction<Integer, Integer> subTwenty = value -> value - 20;
-        JSFunction<Integer, Boolean> isPositive = value -> value >= 0;
+        JSMapping<Integer, Integer> addTwenty = value -> value + 20;
+        JSMapping<Integer, Integer> subTwenty = value -> value - 20;
+        JSMapping<Integer, Boolean> isPositive = value -> value >= 0;
 
         JSConsumer<Integer> print = value -> report("My value: " + value.toString());
         JSConsumer<Integer> print2 = value -> report("My value plus 10: " + Integer.valueOf(value + 10).toString());
 
         var value = supplier.get();
-        report("Supplied value: " + value.toString());
+        report("Supplied value: " + value);
 
         value = addTwenty.apply(value);
         report("Value plus 20: " + value.toString());
@@ -176,7 +176,7 @@ public final class PromiseExample {
     }
 
     private static void runLongRunningPromise(Object lock) {
-        var promise = new JSPromise<>((resolve, reject) -> {
+        new JSPromise<>((resolve, reject) -> {
             report("Long promise exection");
             report("Wait for a while...");
             Window.setTimeout(() -> {
@@ -250,7 +250,7 @@ public final class PromiseExample {
                 var item = value.get(i);
                 var msg = "-- Promise " + i + " " + item.getStatus() + " with: ";
                 if (item.getStatus().stringValue().equals("fulfilled")) {
-                    msg += item.getValue().toString();
+                    msg += item.getValue();
                 } else if (item.getStatus().stringValue().equals("rejected")) {
                     msg += item.getReason().toString();
                 }