initial commit: scaffolding

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diff --git a/node_modules/rxjs/src/internal/observable/zip.ts b/node_modules/rxjs/src/internal/observable/zip.ts
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+import { Observable } from '../Observable';
+import { ObservableInputTuple } from '../types';
+import { innerFrom } from './innerFrom';
+import { argsOrArgArray } from '../util/argsOrArgArray';
+import { EMPTY } from './empty';
+import { createOperatorSubscriber } from '../operators/OperatorSubscriber';
+import { popResultSelector } from '../util/args';
+
+export function zip<A extends readonly unknown[]>(sources: [...ObservableInputTuple<A>]): Observable<A>;
+export function zip<A extends readonly unknown[], R>(
+  sources: [...ObservableInputTuple<A>],
+  resultSelector: (...values: A) => R
+): Observable<R>;
+export function zip<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
+export function zip<A extends readonly unknown[], R>(
+  ...sourcesAndResultSelector: [...ObservableInputTuple<A>, (...values: A) => R]
+): Observable<R>;
+
+/**
+ * Combines multiple Observables to create an Observable whose values are calculated from the values, in order, of each
+ * of its input Observables.
+ *
+ * If the last parameter is a function, this function is used to compute the created value from the input values.
+ * Otherwise, an array of the input values is returned.
+ *
+ * ## Example
+ *
+ * Combine age and name from different sources
+ *
+ * ```ts
+ * import { of, zip, map } from 'rxjs';
+ *
+ * const age$ = of(27, 25, 29);
+ * const name$ = of('Foo', 'Bar', 'Beer');
+ * const isDev$ = of(true, true, false);
+ *
+ * zip(age$, name$, isDev$).pipe(
+ *   map(([age, name, isDev]) => ({ age, name, isDev }))
+ * )
+ * .subscribe(x => console.log(x));
+ *
+ * // Outputs
+ * // { age: 27, name: 'Foo', isDev: true }
+ * // { age: 25, name: 'Bar', isDev: true }
+ * // { age: 29, name: 'Beer', isDev: false }
+ * ```
+ *
+ * @param args Any number of `ObservableInput`s provided either as an array or as an object
+ * to combine with each other.
+ * @return An Observable of array values of the values emitted at the same index from each
+ * individual `ObservableInput`.
+ */
+export function zip(...args: unknown[]): Observable<unknown> {
+  const resultSelector = popResultSelector(args);
+
+  const sources = argsOrArgArray(args) as Observable<unknown>[];
+
+  return sources.length
+    ? new Observable<unknown[]>((subscriber) => {
+        // A collection of buffers of values from each source.
+        // Keyed by the same index with which the sources were passed in.
+        let buffers: unknown[][] = sources.map(() => []);
+
+        // An array of flags of whether or not the sources have completed.
+        // This is used to check to see if we should complete the result.
+        // Keyed by the same index with which the sources were passed in.
+        let completed = sources.map(() => false);
+
+        // When everything is done, release the arrays above.
+        subscriber.add(() => {
+          buffers = completed = null!;
+        });
+
+        // Loop over our sources and subscribe to each one. The index `i` is
+        // especially important here, because we use it in closures below to
+        // access the related buffers and completion properties
+        for (let sourceIndex = 0; !subscriber.closed && sourceIndex < sources.length; sourceIndex++) {
+          innerFrom(sources[sourceIndex]).subscribe(
+            createOperatorSubscriber(
+              subscriber,
+              (value) => {
+                buffers[sourceIndex].push(value);
+                // if every buffer has at least one value in it, then we
+                // can shift out the oldest value from each buffer and emit
+                // them as an array.
+                if (buffers.every((buffer) => buffer.length)) {
+                  const result: any = buffers.map((buffer) => buffer.shift()!);
+                  // Emit the array. If theres' a result selector, use that.
+                  subscriber.next(resultSelector ? resultSelector(...result) : result);
+                  // If any one of the sources is both complete and has an empty buffer
+                  // then we complete the result. This is because we cannot possibly have
+                  // any more values to zip together.
+                  if (buffers.some((buffer, i) => !buffer.length && completed[i])) {
+                    subscriber.complete();
+                  }
+                }
+              },
+              () => {
+                // This source completed. Mark it as complete so we can check it later
+                // if we have to.
+                completed[sourceIndex] = true;
+                // But, if this complete source has nothing in its buffer, then we
+                // can complete the result, because we can't possibly have any more
+                // values from this to zip together with the other values.
+                !buffers[sourceIndex].length && subscriber.complete();
+              }
+            )
+          );
+        }
+
+        // When everything is done, release the arrays above.
+        return () => {
+          buffers = completed = null!;
+        };
+      })
+    : EMPTY;
+}