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27 lines
1.4 KiB
27 lines
1.4 KiB
4 months ago
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import { Observable } from "./Observable.js";
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import { canUseSymbol } from "../common/canUse.js";
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// Generic implementations of Observable.prototype methods like map and
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// filter need to know how to create a new Observable from an Observable
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// subclass (like Concast or ObservableQuery). Those methods assume
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// (perhaps unwisely?) that they can call the subtype's constructor with a
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// Subscriber function, even though the subclass constructor might expect
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// different parameters. Defining this static Symbol.species property on
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// the subclass is a hint to generic Observable code to use the default
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// constructor instead of trying to do `new Subclass(observer => ...)`.
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export function fixObservableSubclass(subclass) {
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function set(key) {
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// Object.defineProperty is necessary because the Symbol.species
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// property is a getter by default in modern JS environments, so we
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// can't assign to it with a normal assignment expression.
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Object.defineProperty(subclass, key, { value: Observable });
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}
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if (canUseSymbol && Symbol.species) {
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set(Symbol.species);
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}
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// The "@@species" string is used as a fake Symbol.species value in some
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// polyfill systems (including the SymbolSpecies variable used by
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// zen-observable), so we should set it as well, to be safe.
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set("@@species");
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return subclass;
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}
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//# sourceMappingURL=subclassing.js.map
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