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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * 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.
 */

/**
 * @fileoverview Polyfill for ES6 extends keyword.
 * @suppress {uselessCode}
 */
'require base';
'require util/objectcreate';
'require es6/util/setprototypeof';


/**
 * Inherit the prototype methods and static methods from one constructor
 * into another.
 *
 * This wires up the prototype chain (like goog.inherits) and copies static
 * properties, for ES6-to-ES{3,5} transpilation.
 *
 * Usage:
 *  *   function ParentClass() {}
 *
 *   // Regular method.
 *   ParentClass.prototype.foo = function(a) {};
 *
 *   // Static method.
 *   ParentClass.bar = function() {};
 *
 *   function ChildClass() {
 *     ParentClass.call(this);
 *   }
 *   $jscomp.inherits(ChildClass, ParentClass);
 *
 *   var child = new ChildClass();
 *   child.foo();
 *   ChildClass.bar();  // Static inheritance.
 * 
 *
 * @param {!Function} childCtor Child class.
 * @param {!Function} parentCtor Parent class.
 * @suppress {strictMissingProperties} 'superClass_' is not defined on Function
 */
$jscomp.inherits = function(childCtor, parentCtor) {
  childCtor.prototype = $jscomp.objectCreate(parentCtor.prototype);
  /** @override */ childCtor.prototype.constructor = childCtor;
  if ($jscomp.setPrototypeOf) {
    // avoid null dereference warning
    /** @const {!Function} */
    var setPrototypeOf = $jscomp.setPrototypeOf;
    setPrototypeOf(childCtor, parentCtor);
  } else {
    // setPrototypeOf is not available so we need to copy the static
    // methods to the child
    for (var p in parentCtor) {
      if (p == 'prototype') {
        // Don't copy parentCtor.prototype to childCtor.
        continue;
      }
      if (Object.defineProperties) {
        var descriptor = Object.getOwnPropertyDescriptor(parentCtor, p);
        if (descriptor) {
          Object.defineProperty(childCtor, p, descriptor);
        }
      } else {
        // Pre-ES5 browser. Just copy with an assignment.
        childCtor[p] = parentCtor[p];
      }
    }
  }

  childCtor.superClass_ = parentCtor.prototype;
};