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asyncMap.ts
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asyncMap.ts
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import { Observable } from "../Observable";
import { asyncMap } from "../asyncMap";
import { itAsync } from "../../../testing";
import { ObservableStream } from "../../../testing/internal";
const wait = (delayMs: number) =>
new Promise<void>((resolve) => setTimeout(resolve, delayMs));
function make1234Observable() {
return new Observable<number>((observer) => {
observer.next(1);
observer.next(2);
setTimeout(() => {
observer.next(3);
setTimeout(() => {
observer.next(4);
observer.complete();
}, 10);
}, 10);
});
}
function rejectExceptions<Args extends any[], Ret>(
reject: (reason: any) => any,
fn: (...args: Args) => Ret
) {
return function () {
try {
return fn.apply(this, arguments);
} catch (error) {
reject(error);
}
} as typeof fn;
}
describe("asyncMap", () => {
itAsync("keeps normal results in order", (resolve, reject) => {
const values: number[] = [];
const mapped: number[] = [];
asyncMap(make1234Observable(), (value) => {
values.push(value);
// Make earlier results take longer than later results.
const delay = 100 - value * 10;
return wait(delay).then(() => value * 2);
}).subscribe({
next(mappedValue) {
mapped.push(mappedValue);
},
error: reject,
complete: rejectExceptions(reject, () => {
expect(values).toEqual([1, 2, 3, 4]);
expect(mapped).toEqual([2, 4, 6, 8]);
resolve();
}),
});
});
itAsync("handles exceptions from mapping functions", (resolve, reject) => {
const triples: number[] = [];
asyncMap(make1234Observable(), (num) => {
if (num === 3) throw new Error("expected");
return num * 3;
}).subscribe({
next: rejectExceptions(reject, (triple) => {
expect(triple).toBeLessThan(9);
triples.push(triple);
}),
error: rejectExceptions(reject, (error) => {
expect(error.message).toBe("expected");
expect(triples).toEqual([3, 6]);
resolve();
}),
});
});
itAsync(
"handles rejected promises from mapping functions",
(resolve, reject) => {
const triples: number[] = [];
asyncMap(make1234Observable(), (num) => {
if (num === 3) return Promise.reject(new Error("expected"));
return num * 3;
}).subscribe({
next: rejectExceptions(reject, (triple) => {
expect(triple).toBeLessThan(9);
triples.push(triple);
}),
error: rejectExceptions(reject, (error) => {
expect(error.message).toBe("expected");
expect(triples).toEqual([3, 6]);
resolve();
}),
});
}
);
itAsync(
"handles async exceptions from mapping functions",
(resolve, reject) => {
const triples: number[] = [];
asyncMap(make1234Observable(), (num) =>
wait(10).then(() => {
if (num === 3) throw new Error("expected");
return num * 3;
})
).subscribe({
next: rejectExceptions(reject, (triple) => {
expect(triple).toBeLessThan(9);
triples.push(triple);
}),
error: rejectExceptions(reject, (error) => {
expect(error.message).toBe("expected");
expect(triples).toEqual([3, 6]);
resolve();
}),
});
}
);
itAsync("handles exceptions from next functions", (resolve, reject) => {
const triples: number[] = [];
asyncMap(make1234Observable(), (num) => {
return num * 3;
}).subscribe({
next(triple) {
triples.push(triple);
// Unfortunately this exception won't be caught by asyncMap, because
// the Observable implementation wraps this next function with its own
// try-catch. Uncomment the remaining lines to make this test more
// meaningful, in the event that this behavior ever changes.
// if (triple === 9) throw new Error("expected");
},
// error: rejectExceptions(reject, error => {
// expect(error.message).toBe("expected");
// expect(triples).toEqual([3, 6, 9]);
// resolve();
// }),
complete: rejectExceptions(reject, () => {
expect(triples).toEqual([3, 6, 9, 12]);
resolve();
}),
});
});
test.each([
["sync", (n: number) => n * 2],
["async", async (n: number) => n * 2],
])("[%s] mapFn maps over values", async (_, mapFn) => {
const observable = new Observable<number>((observer) => {
observer.next(1);
observer.next(2);
setTimeout(() => {
observer.next(3);
setTimeout(() => {
observer.next(4);
observer.complete();
}, 10);
}, 10);
});
const mapped = asyncMap(observable, mapFn);
const stream = new ObservableStream(mapped);
await expect(stream.takeNext()).resolves.toBe(2);
await expect(stream.takeNext()).resolves.toBe(4);
await expect(stream.takeNext()).resolves.toBe(6);
await expect(stream.takeNext()).resolves.toBe(8);
await stream.takeComplete();
});
test.each([["sync"], ["async"]])(
"[%s] mapFn notifies the observer with an error when an error is thrown inside the mapFn",
async (synchronity) => {
const observable = new Observable<number>((observer) => {
observer.next(1);
observer.next(2);
setTimeout(() => {
// this will throw
observer.next(3);
// this will be swallowed and also not call `mapFn` anymore
observer.next(4);
setTimeout(() => {
observer.next(5);
observer.complete();
}, 10);
}, 10);
});
let lastMapped = 0;
const mapped = asyncMap(
observable,
synchronity === "sync"
? (n: number) => {
lastMapped = n;
if (n === 3) throw new Error("expected");
return n * 2;
}
: async (n: number) => {
lastMapped = n;
if (n === 3) throw new Error("expected");
return n * 2;
}
);
const stream = new ObservableStream(mapped);
await expect(stream.takeNext()).resolves.toBe(2);
await expect(stream.takeNext()).resolves.toBe(4);
await expect(stream.takeError()).resolves.toEqual(new Error("expected"));
// no more emits
expect(stream.take()).rejects.toMatch(/timeout/i);
// the observer was closed after the error, so we don't expect `mapFn` to
// be called for values that will not be emitted
expect(lastMapped).toBe(3);
}
);
test.each([
["sync", () => 99],
["async", async () => 99],
])(
"[%s] catchFn notifies the observer with a value when `catchFn` returns a value instead of re-throwing",
async (_, catchFn) => {
const observable = new Observable<number>((observer) => {
observer.next(1);
observer.next(2);
setTimeout(() => {
observer.error(new Error("expected"));
// will be ignored by parent Observable since the observer already closed
observer.next(4);
}, 10);
});
const mapped = asyncMap(observable, (n) => n * 2, catchFn);
const stream = new ObservableStream(mapped);
await expect(stream.takeNext()).resolves.toBe(2);
await expect(stream.takeNext()).resolves.toBe(4);
await expect(stream.takeNext()).resolves.toBe(99);
// even after recovery, further `.next` inside the observer will be ignored
// by the parent Observable itself, so asyncMap cannot do anything about that
expect(stream.take()).rejects.toMatch(/timeout/i);
}
);
test.each([
// prettier-ignore
["sync", () => { throw new Error("another error") }],
// prettier-ignore
["async", async () => { throw new Error("another error") }],
])("[%s] catchFn can map one error to another error", async (_, catchFn) => {
const observable = new Observable<number>((observer) => {
observer.next(1);
observer.next(2);
setTimeout(() => {
observer.error(new Error("expected"));
// will be ignored by Observable since the observer already closed
observer.next(4);
}, 10);
});
const mapped = asyncMap(observable, (n) => n * 2, catchFn);
const stream = new ObservableStream(mapped);
await expect(stream.takeNext()).resolves.toBe(2);
await expect(stream.takeNext()).resolves.toBe(4);
await expect(stream.takeError()).resolves.toEqual(
new Error("another error")
);
// even after recovery, further `.next` inside the observer will be ignored
// by the Observable itself, so asyncMap cannot do anything about that
expect(stream.take()).rejects.toMatch(/timeout/i);
});
});