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// ES2015 Symbol polyfill for environments that do not (or partially) support it
'use strict';
var d = require('d')
, validateSymbol = require('./validate-symbol')
, create = Object.create, defineProperties = Object.defineProperties
, defineProperty = Object.defineProperty, objPrototype = Object.prototype
, NativeSymbol, SymbolPolyfill, HiddenSymbol, globalSymbols = create(null)
, isNativeSafe;
if (typeof Symbol === 'function') {
NativeSymbol = Symbol;
try {
String(NativeSymbol());
isNativeSafe = true;
} catch (ignore) {}
}
var generateName = (function () {
var created = create(null);
return function (desc) {
var postfix = 0, name, ie11BugWorkaround;
while (created[desc + (postfix || '')]) ++postfix;
desc += (postfix || '');
created[desc] = true;
name = '@@' + desc;
defineProperty(objPrototype, name, d.gs(null, function (value) {
// For IE11 issue see:
// https://connect.microsoft.com/IE/feedbackdetail/view/1928508/
// ie11-broken-getters-on-dom-objects
// https://github.com/medikoo/es6-symbol/issues/12
if (ie11BugWorkaround) return;
ie11BugWorkaround = true;
defineProperty(this, name, d(value));
ie11BugWorkaround = false;
}));
return name;
};
}());
// Internal constructor (not one exposed) for creating Symbol instances.
// This one is used to ensure that `someSymbol instanceof Symbol` always return false
HiddenSymbol = function Symbol(description) {
if (this instanceof HiddenSymbol) throw new TypeError('Symbol is not a constructor');
return SymbolPolyfill(description);
};
// Exposed `Symbol` constructor
// (returns instances of HiddenSymbol)
module.exports = SymbolPolyfill = function Symbol(description) {
var symbol;
if (this instanceof Symbol) throw new TypeError('Symbol is not a constructor');
if (isNativeSafe) return NativeSymbol(description);
symbol = create(HiddenSymbol.prototype);
description = (description === undefined ? '' : String(description));
return defineProperties(symbol, {
__description__: d('', description),
__name__: d('', generateName(description))
});
};
defineProperties(SymbolPolyfill, {
for: d(function (key) {
if (globalSymbols[key]) return globalSymbols[key];
return (globalSymbols[key] = SymbolPolyfill(String(key)));
}),
keyFor: d(function (s) {
var key;
validateSymbol(s);
for (key in globalSymbols) if (globalSymbols[key] === s) return key;
}),
// To ensure proper interoperability with other native functions (e.g. Array.from)
// fallback to eventual native implementation of given symbol
hasInstance: d('', (NativeSymbol && NativeSymbol.hasInstance) || SymbolPolyfill('hasInstance')),
isConcatSpreadable: d('', (NativeSymbol && NativeSymbol.isConcatSpreadable) ||
SymbolPolyfill('isConcatSpreadable')),
iterator: d('', (NativeSymbol && NativeSymbol.iterator) || SymbolPolyfill('iterator')),
match: d('', (NativeSymbol && NativeSymbol.match) || SymbolPolyfill('match')),
replace: d('', (NativeSymbol && NativeSymbol.replace) || SymbolPolyfill('replace')),
search: d('', (NativeSymbol && NativeSymbol.search) || SymbolPolyfill('search')),
species: d('', (NativeSymbol && NativeSymbol.species) || SymbolPolyfill('species')),
split: d('', (NativeSymbol && NativeSymbol.split) || SymbolPolyfill('split')),
toPrimitive: d('', (NativeSymbol && NativeSymbol.toPrimitive) || SymbolPolyfill('toPrimitive')),
toStringTag: d('', (NativeSymbol && NativeSymbol.toStringTag) || SymbolPolyfill('toStringTag')),
unscopables: d('', (NativeSymbol && NativeSymbol.unscopables) || SymbolPolyfill('unscopables'))
});
// Internal tweaks for real symbol producer
defineProperties(HiddenSymbol.prototype, {
constructor: d(SymbolPolyfill),
toString: d('', function () { return this.__name__; })
});
// Proper implementation of methods exposed on Symbol.prototype
// They won't be accessible on produced symbol instances as they derive from HiddenSymbol.prototype
defineProperties(SymbolPolyfill.prototype, {
toString: d(function () { return 'Symbol (' + validateSymbol(this).__description__ + ')'; }),
valueOf: d(function () { return validateSymbol(this); })
});
defineProperty(SymbolPolyfill.prototype, SymbolPolyfill.toPrimitive, d('', function () {
var symbol = validateSymbol(this);
if (typeof symbol === 'symbol') return symbol;
return symbol.toString();
}));
defineProperty(SymbolPolyfill.prototype, SymbolPolyfill.toStringTag, d('c', 'Symbol'));
// Proper implementaton of toPrimitive and toStringTag for returned symbol instances
defineProperty(HiddenSymbol.prototype, SymbolPolyfill.toStringTag,
d('c', SymbolPolyfill.prototype[SymbolPolyfill.toStringTag]));
// Note: It's important to define `toPrimitive` as last one, as some implementations
// implement `toPrimitive` natively without implementing `toStringTag` (or other specified symbols)
// And that may invoke error in definition flow:
// See: https://github.com/medikoo/es6-symbol/issues/13#issuecomment-164146149
defineProperty(HiddenSymbol.prototype, SymbolPolyfill.toPrimitive,
d('c', SymbolPolyfill.prototype[SymbolPolyfill.toPrimitive]));
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