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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 Runtime code to store the global object.
 * @suppress {uselessCode}
 */
'require base';

/**
 * Locate and return a reference to the global object.
 *
 * NOTE: This method is marked with `noinline`, because `RemoveUnusedCode` has
 * trouble removing the loop it contains if it gets inlined into the global
 * scope.
 * @param {?Object} passedInThis
 * @return {!Global} The global object.
 * @suppress {undefinedVars|reportUnknownTypes}
 * @noinline
 */
$jscomp.getGlobal = function(passedInThis) {
  var possibleGlobals = [
    // Web Audio Worklets do not have any way to refer to their global object
    // other than `globalThis`.
    // This use of `globalThis` does not prevent removal of the `globalThis`
    // polyfill, because the usage is guarded by a typeof check.
    'object' == typeof globalThis && globalThis,
    // Rhino (used by older Google Docs Script projects) has no `window` or
    // `self`, but `this` from the global scope is the global object. Also,
    // some GWT tests running on Rhino do have a `window` and `self` but, for
    // unknown reasons, see runtime exceptions when we return `window` instead
    // of `passedInThis`.
    // NOTE: If the compiler's output is wrapped in a strict-mode function,
    // this file's code won't actually be executing in global scope, so this
    // value will be undefined.
    passedInThis,
    // Browser windows always have `window`
    'object' == typeof window && window,
    // WebWorkers have `self`
    'object' == typeof self && self,
    // NodeJS has `global`
    'object' == typeof global && global,
  ];
  for (var i = 0; i < possibleGlobals.length; ++i) {
    var maybeGlobal = possibleGlobals[i];
    // It can happen that an environment has, for example, both `global` and
    // `window` defined in the global scope, but one of them isn't actually
    // the global object, so check that it really seems to be the global object.
    // We use `Math` to check for this because it's only 4 characters long,
    // exists in all possible JS environments, and doesn't have the problematic
    // equality behavior of `NaN`.
    if (maybeGlobal && maybeGlobal['Math'] == Math) {
      return /** @type {!Global} */ (maybeGlobal);
    }
  }
  // Throw an exception if we cannot find the global object.
  // We have to be sneaky about it, otherwise the compiler will think this code
  // has a side effect (throwing an exception) that prevents it from being
  // removed, even when all usages of `$jscomp.global` get removed.
  // Casting through unknown is necessary to keep the compiler from rejecting
  // this code.
  return /** @type {!Global} */ (
      /** @type {?} */ ({
        valueOf: function() {
          throw new Error('Cannot find global object');
        }
      }.valueOf()));
};


/**
 * The global object.
 * @const {!Global}
 */
$jscomp.global = $jscomp.getGlobal(this);