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node_modules/rxjs/src/internal/operators/map.ts

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+import { Operator } from '../Operator';
+import { Subscriber } from '../Subscriber';
+import { Observable } from '../Observable';
+import { OperatorFunction } from '../types';
+
+/**
+ * Applies a given `project` function to each value emitted by the source
+ * Observable, and emits the resulting values as an Observable.
+ *
+ * <span class="informal">Like [Array.prototype.map()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map),
+ * it passes each source value through a transformation function to get
+ * corresponding output values.</span>
+ *
+ * ![](map.png)
+ *
+ * Similar to the well known `Array.prototype.map` function, this operator
+ * applies a projection to each value and emits that projection in the output
+ * Observable.
+ *
+ * ## Example
+ * Map every click to the clientX position of that click
+ * ```ts
+ * import { fromEvent } from 'rxjs';
+ * import { map } from 'rxjs/operators';
+ *
+ * const clicks = fromEvent(document, 'click');
+ * const positions = clicks.pipe(map(ev => ev.clientX));
+ * positions.subscribe(x => console.log(x));
+ * ```
+ *
+ * @see {@link mapTo}
+ * @see {@link pluck}
+ *
+ * @param {function(value: T, index: number): R} project The function to apply
+ * to each `value` emitted by the source Observable. The `index` parameter is
+ * the number `i` for the i-th emission that has happened since the
+ * subscription, starting from the number `0`.
+ * @param {any} [thisArg] An optional argument to define what `this` is in the
+ * `project` function.
+ * @return {Observable<R>} An Observable that emits the values from the source
+ * Observable transformed by the given `project` function.
+ * @method map
+ * @owner Observable
+ */
+export function map<T, R>(project: (value: T, index: number) => R, thisArg?: any): OperatorFunction<T, R> {
+  return function mapOperation(source: Observable<T>): Observable<R> {
+    if (typeof project !== 'function') {
+      throw new TypeError('argument is not a function. Are you looking for `mapTo()`?');
+    }
+    return source.lift(new MapOperator(project, thisArg));
+  };
+}
+
+export class MapOperator<T, R> implements Operator<T, R> {
+  constructor(private project: (value: T, index: number) => R, private thisArg: any) {
+  }
+
+  call(subscriber: Subscriber<R>, source: any): any {
+    return source.subscribe(new MapSubscriber(subscriber, this.project, this.thisArg));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class MapSubscriber<T, R> extends Subscriber<T> {
+  count: number = 0;
+  private thisArg: any;
+
+  constructor(destination: Subscriber<R>,
+              private project: (value: T, index: number) => R,
+              thisArg: any) {
+    super(destination);
+    this.thisArg = thisArg || this;
+  }
+
+  // NOTE: This looks unoptimized, but it's actually purposefully NOT
+  // using try/catch optimizations.
+  protected _next(value: T) {
+    let result: R;
+    try {
+      result = this.project.call(this.thisArg, value, this.count++);
+    } catch (err) {
+      this.destination.error(err);
+      return;
+    }
+    this.destination.next(result);
+  }
+}