console.clear()

​

console.log('start')

​

const { Subject } = rxjs

const { concatMap, mergeMap, switchMap, map } = rxjs.operators

​

const subject = new Subject()

​

subject

  .pipe(

    concatMap(obj => { // concatMap, mergeMap, switchMap で結果が変わる

      return httpGet(obj.url, obj.delay)

    }),

    map(res => JSON.parse(res).ResultData)

  )

  .subscribe(value => {

    console.log(value)

  })

​

subject.next({ url: 'http://foo', delay: 500 })

subject.next({ url: 'http://bar', delay: 300 })

subject.next({ url: 'http://baz', delay: 100 })

​

​

function httpGet(url, delay) {

  return new Promise(resolve => {

    setTimeout(() => {

      const obj = { ResultData: url + ' -> resolved' }

      resolve(JSON.stringify(obj))

    }, delay)

  })

}