rxjs里merge operators的用法stream是lazy的，no subscription, no calc

stream是lazy的，no subscription, no calculation occurs.

作用：Flattens multiple Observables together by blending their values into one Observable.

例子：

 const clicks = fromEvent(document, 'click');
    const timer = interval(1000);
    const clicksOrTimer = merge(clicks, timer);
    clicksOrTimer.subscribe(x => console.log('jerry: ' + x));

测试结果：每隔1秒钟Observable emit一个值递增的整数。然后如果我点击UI，会显示一个[object MouseEvent]的事件：

const timer1 = interval(1000).pipe(take(10));
const timer2 = interval(1000).pipe(take(10));
const timer3 = interval(1000).pipe(take(10));
const concurrent = 3; // the argument
const merged = merge(timer1, timer2, timer3, concurrent);
merged.subscribe(x => console.log('diablo: '
 + x));

每秒同时emit 三个值：

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