5. 创建 Observable

var button = document.querySelector('button');
button.addEventListener('click', () => console.log('Clicked!'));

<script src='./lib/rxjs.6.3.3.umd.min.js'></script>
<script>
const { fromEvent } = rxjs;

const button = document.querySelector('button');
fromEvent(button, 'click')
  .subscribe(() => console.log('Clicked!'));
</script>

  // Observer 是一个对象，这个对象具有三个方法，分别是 next, error, complete
  // 建立 Observable 最简单方法是用 create 方法
  // create 接收一个回调函数，把observer作为参数
  const observer = {
    next: value => {
      console.log(`observer:` + value)
    },
    error: error => {
      console.log('Error:', error);
    },
    complete: () => {
      console.log('complete');
    }
  }

  var observable = rxjs.Observable
    .create(observer => {
      observer.next('Jerry');
      observer.next('Anna');
      observer.complete();
      observer.next('not work');
    })

  // 建立观察者来订阅 observable
  // 订阅一个 Observable 就像是执行一个 function
  observable.subscribe(
    observer
  )

  const {from} = rxjs;

  function f() {
    return from(arguments);
  }

  const observer = {
    next: value => {
      console.log('Next: ' + value);
    },
    error: error => {
      console.log('Error:', error);
    },
    complete: () => {
      console.log('Complete');
    }
  }

  // Array Like Object
  f(1, 2, 3).subscribe(observer);

  // string
  from('foo').subscribe(observer);

  // Set, any iterable object
  const s = new Set(['foo', window]);
  from(s).subscribe(observer);

  // Promise
  const source = from(new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve('Hello RxJS!');
      }, 3000)
    }))

  source.subscribe(observer);