Answer 1

function multiRequest(urls, maxNum) {
        return new Promise((res, rej) => {
          const tasksLength = urls.length
          const result = []
          let i = 0
          let done = 0
          function runTask() {
            if(i >= tasksLength) return

            const curIndex = i
            const url = urls[curIndex]
            fetch(url).then(res => res.json()).then((value) => {
              result[curIndex] = value
              done++
              if(done === tasksLength) {
                res(result)
                return
              }
              runTask()
            }).catch(err => {
              rej(err)
            })
            i++
          }

          while(maxNum !== 0) {
            runTask()
            maxNum--
          }
        })
      }