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node_modules/rxjs/src/internal/lastValueFrom.ts

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+import { Observable } from './Observable';
+import { EmptyError } from './util/EmptyError';
+
+export interface LastValueFromConfig<T> {
+  defaultValue: T;
+}
+
+export function lastValueFrom<T, D>(source: Observable<T>, config: LastValueFromConfig<D>): Promise<T | D>;
+export function lastValueFrom<T>(source: Observable<T>): Promise<T>;
+
+/**
+ * Converts an observable to a promise by subscribing to the observable,
+ * waiting for it to complete, and resolving the returned promise with the
+ * last value from the observed stream.
+ *
+ * If the observable stream completes before any values were emitted, the
+ * returned promise will reject with {@link EmptyError} or will resolve
+ * with the default value if a default was specified.
+ *
+ * If the observable stream emits an error, the returned promise will reject
+ * with that error.
+ *
+ * **WARNING**: Only use this with observables you *know* will complete. If the source
+ * observable does not complete, you will end up with a promise that is hung up, and
+ * potentially all of the state of an async function hanging out in memory. To avoid
+ * this situation, look into adding something like {@link timeout}, {@link take},
+ * {@link takeWhile}, or {@link takeUntil} amongst others.
+ *
+ * ## Example
+ *
+ * Wait for the last value from a stream and emit it from a promise in
+ * an async function
+ *
+ * ```ts
+ * import { interval, take, lastValueFrom } from 'rxjs';
+ *
+ * async function execute() {
+ *   const source$ = interval(2000).pipe(take(10));
+ *   const finalNumber = await lastValueFrom(source$);
+ *   console.log(`The final number is ${ finalNumber }`);
+ * }
+ *
+ * execute();
+ *
+ * // Expected output:
+ * // 'The final number is 9'
+ * ```
+ *
+ * @see {@link firstValueFrom}
+ *
+ * @param source the observable to convert to a promise
+ * @param config a configuration object to define the `defaultValue` to use if the source completes without emitting a value
+ */
+export function lastValueFrom<T, D>(source: Observable<T>, config?: LastValueFromConfig<D>): Promise<T | D> {
+  const hasConfig = typeof config === 'object';
+  return new Promise<T | D>((resolve, reject) => {
+    let _hasValue = false;
+    let _value: T;
+    source.subscribe({
+      next: (value) => {
+        _value = value;
+        _hasValue = true;
+      },
+      error: reject,
+      complete: () => {
+        if (_hasValue) {
+          resolve(_value);
+        } else if (hasConfig) {
+          resolve(config!.defaultValue);
+        } else {
+          reject(new EmptyError());
+        }
+      },
+    });
+  });
+}