wishthis/node_modules/es6-symbol/polyfill.js
2022-01-21 09:28:41 +01:00

87 lines
3.2 KiB
JavaScript

// ES2015 Symbol polyfill for environments that do not (or partially) support it
"use strict";
var d = require("d")
, validateSymbol = require("./validate-symbol")
, NativeSymbol = require("ext/global-this").Symbol
, generateName = require("./lib/private/generate-name")
, setupStandardSymbols = require("./lib/private/setup/standard-symbols")
, setupSymbolRegistry = require("./lib/private/setup/symbol-registry");
var create = Object.create
, defineProperties = Object.defineProperties
, defineProperty = Object.defineProperty;
var SymbolPolyfill, HiddenSymbol, isNativeSafe;
if (typeof NativeSymbol === "function") {
try {
String(NativeSymbol());
isNativeSafe = true;
} catch (ignore) {}
} else {
NativeSymbol = null;
}
// 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))
});
};
setupStandardSymbols(SymbolPolyfill);
setupSymbolRegistry(SymbolPolyfill);
// 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])
);