docs(operators): add documentation for concat

Author: sumitarora

src/operator-docs/combination/concat.ts

@@ -1,6 +1,116 @@
 import { OperatorDoc } from '../operator.model';
 
 export const concat: OperatorDoc = {
-  'name': 'concat',
-  'operatorType': 'combination'
+  name: 'concat',
+  operatorType: 'combination',
+  signature:
+    'public static concat(input1: ObservableInput, input2: ObservableInput, scheduler: Scheduler): Observable',
+  parameters: [
+    {
+      name: 'input1',
+      type: 'ObservableInput',
+      attribute: '',
+      description: 'An input Observable to concatenate with others.'
+    },
+    {
+      name: 'input2',
+      type: 'ObservableInput',
+      attribute: '',
+      description:
+        'An input Observable to concatenate with others. More than one input Observables may be given as argument.'
+    },
+    {
+      name: 'scheduler',
+      type: 'Scheduler',
+      attribute: 'optional default: null',
+      description:
+        'An optional IScheduler to schedule each Observable subscription on.'
+    }
+  ],
+  marbleUrl: 'http://reactivex.io/rxjs/img/concat.png',
+  shortDescription: {
+    description:
+      'Creates an output Observable which sequentially emits all values from given Observable and then moves on to the next.',
+    extras: [
+      {
+        type: 'Tip',
+        text:
+          'Concatenates multiple Observables together by sequentially emitting their values, one Observable after the other.'
+      }
+    ]
+  },
+  walkthrough: {
+    description: `
+      <p><span class='markdown-code'>concat</span> joins multiple Observables together, by subscribing to them one at a time and
+      merging their results into the output Observable. You can pass either an array of
+      Observables, or put them directly as arguments. Passing an empty array will result
+      in Observable that completes immediately.</p>
+
+      <p><span class='markdown-code'>concat</span> will subscribe to first input Observable and emit all its values, without
+      changing or affecting them in any way. When that Observable completes, it will
+      subscribe to then next Observable passed and, again, emit its values. This will be
+      repeated, until the operator runs out of Observables. When last input Observable completes,
+      <span class='markdown-code'>concat</span> will complete as well. At any given moment only one Observable passed to operator
+      emits values. If you would like to emit values from passed Observables concurrently, check out
+      <a href='/#/operators/merge' class='markdown-code'>merge</a> instead, especially with optional
+      <span class='markdown-code'>concurrent</span> parameter.
+      As a matter of fact, <span class='markdown-code'>concat</span> is an equivalent of
+      <a href='/#/operators/merge' class='markdown-code'>merge</a> operator with
+      <span class='markdown-code'>concurrent</span> parameter set to <span class='markdown-code'>1</span>.</p>
+
+      <p>Note that if some input Observable never completes, <span class='markdown-code'>concat</span> will also never complete
+      and Observables following the one that did not complete will never be subscribed. On the other
+      hand, if some Observable simply completes immediately after it is subscribed, it will be
+      invisible for <span class='markdown-code'>concat</span>, which will just move on to the next Observable.</p>
+
+      <p>If any Observable in chain errors, instead of passing control to the next Observable,
+      <span class='markdown-code'>concat</span> will error immediately as well. Observables that would be subscribed after
+      the one that emitted error, never will.</p>
+
+      <p>If you pass to <span class='markdown-code'>concat</span> the same Observable many times, its stream of values
+      will be 'replayed' on every subscription, which means you can repeat given Observable
+      as many times as you like. If passing the same Observable to <span class='markdown-code'>concat</span> 1000 times becomes tedious,
+      you can always use <span class='markdown-code'>repeat</span>.</p>
+    `
+  },
+  examples: [
+    {
+      name:
+        'Concatenate a timer counting from 0 to 3 with a synchronous sequence from 1 to 10',
+      code: `
+      const timer = Rx.Observable.interval(1000).take(4);
+      const sequence = Rx.Observable.range(1, 10);
+      const result = Rx.Observable.concat(timer, sequence);
+      result.subscribe(x => console.log(x));
+
+      // results in:
+      // 0 -1000ms-> 1 -1000ms-> 2 -1000ms-> 3 -immediate-> 1 ... 10
+    `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/doqoyimaxu/embed?js,console'
+      }
+    },
+    {
+      name: 'Concatenate an array of 3 Observables',
+      code: `
+      const timer1 = Rx.Observable.interval(1000).take(10);
+      const timer2 = Rx.Observable.interval(2000).take(6);
+      const timer3 = Rx.Observable.interval(500).take(10);
+      const result = timer1.concat(timer2, timer3);
+      result.subscribe(x => console.log(x));
+
+      // results in the following:
+      // (Prints to console sequentially)
+      // -1000ms-> 0 -1000ms-> 1 -1000ms-> ... 9
+      // -2000ms-> 0 -2000ms-> 1 -2000ms-> ... 5
+      // -500ms-> 0 -500ms-> 1 -500ms-> ... 9
+    `,
+      externalLink: {
+        platform: 'JSBin',
+        url: 'http://jsbin.com/decaromone/1/embed?js,console'
+      }
+    }
+  ],
+  relatedOperators: ['concatAll', 'concatMap', 'concatMapTo']
 };