87 lines
3.2 KiB
JavaScript
87 lines
3.2 KiB
JavaScript
// ES2015 Symbol polyfill for environments that do not (or partially) support it
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"use strict";
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var d = require("d")
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, validateSymbol = require("./validate-symbol")
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, NativeSymbol = require("ext/global-this").Symbol
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, generateName = require("./lib/private/generate-name")
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, setupStandardSymbols = require("./lib/private/setup/standard-symbols")
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, setupSymbolRegistry = require("./lib/private/setup/symbol-registry");
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var create = Object.create
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, defineProperties = Object.defineProperties
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, defineProperty = Object.defineProperty;
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var SymbolPolyfill, HiddenSymbol, isNativeSafe;
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if (typeof NativeSymbol === "function") {
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try {
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String(NativeSymbol());
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isNativeSafe = true;
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} catch (ignore) {}
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} else {
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NativeSymbol = null;
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}
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// Internal constructor (not one exposed) for creating Symbol instances.
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// This one is used to ensure that `someSymbol instanceof Symbol` always return false
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HiddenSymbol = function Symbol(description) {
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if (this instanceof HiddenSymbol) throw new TypeError("Symbol is not a constructor");
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return SymbolPolyfill(description);
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};
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// Exposed `Symbol` constructor
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// (returns instances of HiddenSymbol)
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module.exports = SymbolPolyfill = function Symbol(description) {
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var symbol;
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if (this instanceof Symbol) throw new TypeError("Symbol is not a constructor");
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if (isNativeSafe) return NativeSymbol(description);
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symbol = create(HiddenSymbol.prototype);
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description = description === undefined ? "" : String(description);
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return defineProperties(symbol, {
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__description__: d("", description),
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__name__: d("", generateName(description))
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});
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};
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setupStandardSymbols(SymbolPolyfill);
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setupSymbolRegistry(SymbolPolyfill);
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// Internal tweaks for real symbol producer
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defineProperties(HiddenSymbol.prototype, {
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constructor: d(SymbolPolyfill),
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toString: d("", function () { return this.__name__; })
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});
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// Proper implementation of methods exposed on Symbol.prototype
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// They won't be accessible on produced symbol instances as they derive from HiddenSymbol.prototype
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defineProperties(SymbolPolyfill.prototype, {
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toString: d(function () { return "Symbol (" + validateSymbol(this).__description__ + ")"; }),
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valueOf: d(function () { return validateSymbol(this); })
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});
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defineProperty(
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SymbolPolyfill.prototype,
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SymbolPolyfill.toPrimitive,
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d("", function () {
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var symbol = validateSymbol(this);
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if (typeof symbol === "symbol") return symbol;
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return symbol.toString();
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})
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);
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defineProperty(SymbolPolyfill.prototype, SymbolPolyfill.toStringTag, d("c", "Symbol"));
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// Proper implementaton of toPrimitive and toStringTag for returned symbol instances
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defineProperty(
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HiddenSymbol.prototype, SymbolPolyfill.toStringTag,
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d("c", SymbolPolyfill.prototype[SymbolPolyfill.toStringTag])
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);
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// Note: It's important to define `toPrimitive` as last one, as some implementations
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// implement `toPrimitive` natively without implementing `toStringTag` (or other specified symbols)
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// And that may invoke error in definition flow:
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// See: https://github.com/medikoo/es6-symbol/issues/13#issuecomment-164146149
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defineProperty(
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HiddenSymbol.prototype, SymbolPolyfill.toPrimitive,
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d("c", SymbolPolyfill.prototype[SymbolPolyfill.toPrimitive])
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);
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