121 lines
3.6 KiB
JavaScript
121 lines
3.6 KiB
JavaScript
/**
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* Global scope handling
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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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// retrieve global scope; works with ES5 strict mode
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(0,eval)( 'var _the_global=this' );
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// prototype to allow us to augment the global scope for our own purposes
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// without polluting the global scope
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function _G() {}
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_G.prototype = _the_global;
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/**
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* Provides access to and augmentation of global variables
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*
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* This provides a static method to consistently provide access to the
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* object representing the global scope, regardless of environment. Through
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* instantiation, its API permits augmenting a local object whose prototype
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* is the global scope, providing alternatives to variables that do not
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* exist.
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*/
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function Global()
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{
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// allows omitting `new` keyword, consistent with ease.js style
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if ( !( this instanceof Global ) )
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{
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return new Global();
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}
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// allows us to extend the global object without actually polluting the
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// global scope
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this._global = new _G();
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}
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/**
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* Provides consistent access to the global scope through all ECMAScript
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* versions, for any root variable name, and works with ES5 strict mode.
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*
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* As an example, Node.js exposes the variable `root` to represent global
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* scope, but browsers expose `window`. Further, ES5 strict mode will provde
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* an error when checking whether `typeof SomeGlobalVar === 'undefined'`.
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*
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* @return {Object} global object
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*/
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Global.expose = function()
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{
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return _the_global;
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};
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Global.prototype = {
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/**
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* Provide a value for the provided global variable name if it is not
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* defined
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*
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* A function returning the value to assign to NAME should be provided,
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* ensuring that the alternative is never even evaluated unless it is
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* needed.
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*
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* The global scope will not be polluted with this alternative;
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* consequently, you must access the value using the `get` method.
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*
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* @param {string} name global variable name
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* @param {function()} f function returning value to assign
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*
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* @return {Global} self
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*/
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provideAlt: function( name, f )
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{
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if ( typeof this._global[ name ] !== 'undefined' )
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{
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return;
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}
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this._global[ name ] = f();
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return this;
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},
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/**
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* Retrieve global value or provided alternative
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*
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* This will take into account values provided via `provideAlt`; if no
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* alternative was provided, the request will be deleagated to the
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* global variable NAME, which may or may not be undefined.
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*
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* No error will be thrown if NAME is not globally defined.
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*
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* @param {string} name global variable name
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*
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* @return {*} value associated with global variable NAME or
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* its provided alternative
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*/
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get: function( name )
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{
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return this._global[ name ];
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},
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};
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module.exports = Global;
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