67 lines
2.6 KiB
JavaScript
67 lines
2.6 KiB
JavaScript
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/**
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* Forward-compatible subset of ES6 Symbol for pre-ES6 environments
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*
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* Copyright (C) 2014 Free Software Foundation, Inc.
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*
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* This file is part of GNU ease.js.
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*
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* ease.js is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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* This is *not* intended to be a complete implementation; it merely
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* performs what is needed for ease.js. In particular, this pre-ES6
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* implementation will simply generate a random string to be used as a key;
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* the caller is expected to add the key to the destination object as
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* non-enumerable, if supported by the environment.
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*/
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// ensures that, so long as these methods have not been overwritten by the
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// time ease.js is loaded, we will maintain a proper reference
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var _random = Math.random,
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_floor = Math.floor;
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// prefix used for all generated symbol strings (this string is highly
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// unlikely to exist in practice); it will produce a string containing a
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// non-printable ASCII character that is *not* the null byte
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var _root = ' ' + String.fromCharCode(
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_floor( _random() * 10 ) % 31 + 1
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) + '$';
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/**
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* Generate a pseudo-random string (with a common prefix) to be used as an
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* object key
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*
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* The returned key is unique so long as Math.{random,floor} are reliable.
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* This will be true so long as (1) the runtime provides a reliable
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* implementation and (2) Math.{floor,random} have not been overwritten at
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* the time that this module is loaded. This module stores an internal
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* reference to this methods, so malicious code loaded after this module
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* will not be able to compromise the return value.
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*
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* Note that the returned string is not wholly random: a common prefix is
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* used to ensure that collisions with other keys on objects is highly
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* unlikely; you should not rely on this behavior, though, as it is an
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* implementation detail that may change in the future.
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*
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* @return {string} pseudo-random string with common prefix
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*/
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function FallbackSymbol()
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{
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return _root + _floor( _random() * 1e8 );
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}
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module.exports = FallbackSymbol;
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