DOM: Implement the `take()` Observable operator
This CL implements the semantics specified in
https://wicg.github.io/observable/#dom-observable-take.
See https://github.com/WICG/observable/pull/113.
For WPTs:
Co-authored-by: ben@benlesh.com
R=masonf@chromium.org
Bug: 40282760
Change-Id: Iaaa957c20db8df54619b65d98ca54385d5ee79a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5292297
Reviewed-by: Mason Freed <masonf@chromium.org>
Commit-Queue: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1263804}
diff --git a/dom/observable/tentative/observable-take.any.js b/dom/observable/tentative/observable-take.any.js
new file mode 100644
index 0000000..8350d02
--- /dev/null
+++ b/dom/observable/tentative/observable-take.any.js
@@ -0,0 +1,108 @@
+test(() => {
+ const results = [];
+ const source = new Observable(subscriber => {
+ subscriber.addTeardown(() => results.push("source teardown"));
+ subscriber.next(1);
+ subscriber.next(2);
+ subscriber.next(3);
+ subscriber.complete();
+ });
+
+ const result = source.take(2);
+
+ result.subscribe({
+ next: v => results.push(v),
+ error: e => results.push(e),
+ complete: () => results.push("complete"),
+ });
+
+ assert_array_equals(results, [1, 2, "source teardown", "complete"]);
+}, "take(): Takes the first N values from the source observable, then completes");
+
+test(() => {
+ const results = [];
+ const source = new Observable(subscriber => {
+ subscriber.addTeardown(() => results.push("source teardown"));
+ subscriber.next(1);
+ subscriber.next(2);
+ subscriber.next(3);
+ subscriber.complete();
+ });
+
+ const result = source.take(5);
+
+ result.subscribe({
+ next: v => results.push(v),
+ error: e => results.push(e),
+ complete: () => results.push("complete"),
+ });
+
+ assert_array_equals(results, [1, 2, 3, "source teardown", "complete"],
+ "complete() is immediately forwarded");
+}, "take(): Forwards complete()s that happen before the take count is met, " +
+ "and unsubscribes from source Observable");
+
+test(() => {
+ const results = [];
+ const error = new Error('source error');
+ const source = new Observable(subscriber => {
+ subscriber.next(1);
+ subscriber.error(error);
+ });
+
+ const result = source.take(100);
+
+ result.subscribe({
+ next: v => results.push(v),
+ error: e => results.push(e),
+ complete: () => results.push("complete"),
+ });
+
+ assert_array_equals(results, [1, error], "Errors are forwarded");
+}, "take(): Should forward errors from the source observable");
+
+test(() => {
+ const results = [];
+ const source = new Observable((subscriber) => {
+ results.push("source subscribe");
+ subscriber.next(1);
+ subscriber.next(2);
+ subscriber.next(3);
+ subscriber.complete();
+ });
+
+ const result = source.take(0);
+
+ result.subscribe({
+ next: v => results.push(v),
+ error: e => results.push(e),
+ complete: () => results.push("complete"),
+ });
+
+ assert_array_equals(results, ["complete"]);
+}, "take(): take(0) should not subscribe to the source observable, and " +
+ "should return an observable that immediately completes");
+
+test(() => {
+ const results = [];
+ const source = new Observable((subscriber) => {
+ results.push("source subscribe");
+ subscriber.next(1);
+ subscriber.next(2);
+ subscriber.next(3);
+ subscriber.complete();
+ });
+
+ // Per WebIDL, `-1` passed into an `unsigned long long` gets wrapped around
+ // into the maximum value (18446744073709551615), which means the `result`
+ // Observable captures everything that `source` does.
+ const result = source.take(-1);
+
+ result.subscribe({
+ next: v => results.push(v),
+ error: e => results.push(e),
+ complete: () => results.push("complete"),
+ });
+
+ assert_array_equals(results, ["source subscribe", 1, 2, 3, "complete"]);
+}, "take(): Negative count is treated as maximum value");
