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/*
 * Copyright 2015 Google Inc.
 *
 * 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.
 */
package jsinterop.annotations;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * JsFunction marks a functional interface as being the definition of a JavaScript function.
 *
 * There are some limitations exists on JsFunction to make them practical and efficient:
 *
 * 

 *   A JsFunction interface cannot extend any other interfaces.
 *   
A class may not implement more than one JsFunction interface.
 *   
A class that implements a JsFunction type cannot be a {@link JsType} (directly or
 *       indirectly).
 *   
Fields and defender methods of the interfaces should be marked with {@link JsOverlay} and
 *       cannot be overridden by the implementations.
 * 
 *
 * As a best practice, we also recommend marking JsFunction interfaces with FunctionalInterface
 * to get improved checking in IDEs.
 *
 * 
Instanceof and Castability:
 *
 * Instanceof and casting for JsFunction is effectively a JavaScript {@code typeof} check to
 * determine if the instance is a function.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
public @interface JsFunction {}