fetch.js

array = (new Array(5000)).fill(1)
task = array.map(item => {
  return fetch('http://localhost:5000/diandian-landing-payment/us-central1/api/test')
})

duplicated = []

Promise
.all(task)
.then(result => result.map(item => item.json()))
.then(result => result.map(item => {
  return item.orderId
}))
.then(result => {
  duplicated = result.filter((item, index) => {
    if (result.indexOf(item) !== result.lastIndexOf(item) && result.indexOf(item) === index) {
      return true
    }
    
    return false
  })
  
  console.log(duplicated)
})