Add a delay between each ajax call

delay.js

export default function delay(ms) {
  return new Promise(resolve => {
    setTimeout(resolve, ms)
  })
}

index.js

import series from 'p-series'

series([
  () => requestX(),
  () => delay(1000),
  () => requestY(),
  () => delay(1000),
  () => requextZ()
]).then(([resX, resY, resZ]) => {  
  // Do something
}, err => {
  // Do something with the error
})