docs(operators): add documentation for operator switchMap

Author: mustafamg

src/operator-docs/transformation/switchMap.ts

@@ -1,6 +1,69 @@
 import { OperatorDoc } from '../operator.model';
 
 export const switchMap: OperatorDoc = {
-  'name': 'switchMap',
-  'operatorType': 'transformation'
+  name: 'switchMap',
+  operatorType: 'transformation',
+  signature: `switchMap(project: (value: T, index: number) => ObservableInput<I>,
+  resultSelector: (outerValue: T, innerValue: I, outerIndex: number, innerIndex: number) => R): Observable`,
+  parameters: [
+    {
+      name: 'project',
+      type: 'function(value: T, index: number): ObservableInput',
+      attribute: '',
+      description: `A function that, when applied to an item emitted by the source
+       Observable, returns an Observable.`
+    },
+    {
+      name: 'resultSelector',
+      type:
+        'function(outerValue: T, innerValue: I, outerIndex: number, innerIndex: number): any',
+      attribute: 'optional',
+      description: `A function to produce the value on the output Observable based on the values
+      and the indices of the source (outer) emission and the inner Observable
+      emission. The arguments passed to this function are:
+      - 'outerValue': the value that came from the source.
+      - 'innerValue': the value that came from the projected Observable.
+      - 'outerIndex': the "index" of the value that came from the source.
+      - 'innerIndex': the "index" of the value from the projected Observable.`
+    }
+  ],
+  marbleUrl: 'http://reactivex.io/rxjs/img/switchMap.png',
+  shortDescription: {
+    description: `Projects each source value to an Observable which is merged in the output
+    Observable, emitting values only from the most recently projected Observable.
+
+    <span class="informal">Maps each value to an Observable, then flattens all of
+    these inner Observables using <code>switch</code>.</span>`
+  },
+  walkthrough: {
+    description: `Returns an Observable that emits items based on applying a function that you
+    supply to each item emitted by the source Observable, where that function
+    returns an (so-called "inner") Observable. Each time it observes one of these
+    inner Observables, the output Observable begins emitting the items emitted by
+    that inner Observable. When a new inner Observable is emitted, <code>switchMap</code>
+    stops emitting items from the earlier-emitted inner Observable and begins
+    emitting items from the new one. It continues to behave like this for
+    subsequent inner Observables.`
+  },
+  examples: [
+    {
+      name: 'Rerun an interval Observable on every click even',
+      code: `
+      const clicks = Rx.Observable.fromEvent(document, 'click');
+      const result = clicks.switchMap((ev) => Rx.Observable.interval(1000));
+      result.subscribe(x => console.log(x));
+      `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/yehawof/edit?js,console,output'
+      }
+    }
+  ],
+  relatedOperators: [
+    'concatMap',
+    'exhaustMap',
+    'mergeMap',
+    'switch',
+    'switchMapTo'
+  ]
 };