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44 lines
2.0 KiB
44 lines
2.0 KiB
5 months ago
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import { Observable } from "./Observable.js";
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// Like Observable.prototype.map, except that the mapping function can
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// optionally return a Promise (or be async).
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export function asyncMap(observable, mapFn, catchFn) {
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return new Observable(function (observer) {
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var promiseQueue = {
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// Normally we would initialize promiseQueue to Promise.resolve(), but
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// in this case, for backwards compatibility, we need to be careful to
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// invoke the first callback synchronously.
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then: function (callback) {
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return new Promise(function (resolve) { return resolve(callback()); });
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},
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};
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function makeCallback(examiner, key) {
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return function (arg) {
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if (examiner) {
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var both = function () {
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// If the observer is closed, we don't want to continue calling the
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// mapping function - it's result will be swallowed anyways.
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return observer.closed ?
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/* will be swallowed */ 0
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: examiner(arg);
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};
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promiseQueue = promiseQueue.then(both, both).then(function (result) { return observer.next(result); }, function (error) { return observer.error(error); });
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}
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else {
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observer[key](arg);
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}
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};
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}
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var handler = {
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next: makeCallback(mapFn, "next"),
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error: makeCallback(catchFn, "error"),
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complete: function () {
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// no need to reassign `promiseQueue`, after `observer.complete`,
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// the observer will be closed and short-circuit everything anyways
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/*promiseQueue = */ promiseQueue.then(function () { return observer.complete(); });
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},
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};
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var sub = observable.subscribe(handler);
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return function () { return sub.unsubscribe(); };
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});
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}
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//# sourceMappingURL=asyncMap.js.map
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