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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 2022 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 'at' methods in String, Array and TypeArray.
 * @suppress {uselessCode}
 */
'require base';
'require es6/math/trunc';

/**
 * Polyfills (Array|String|TypedArray).prototype.at.
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at
 *
 * @this {!IArrayLike}
 * @param {number} index
 * @return {T}
 * @template T
 */
$jscomp.atMethod = function(index) {
  var array = this;

  var indexValue = Math.trunc(index) || 0;
  // Allow negative indexing from the end
  if (indexValue < 0) indexValue += array.length;
  // OOB access is guaranteed to return undefined
  if (indexValue < 0 || indexValue >= array.length) return undefined;
  // Otherwise, this is just normal property access
  return array[indexValue];
};