jsonp.js

function encodeUrl(url, params) {
  let paramStr = ''
  for(let key in params) {
    paramStr+=key+'='+params[key]+'&'
  }
  return url+'?'+paramStr.slice(0, paramStr.length-1)
}

function jsonp(url, params, cb) {
  url = encodeUrl(url, params)

  var script = document.createElement('script')
  script.setAttribute('src', url)
  document.querySelector('body').appendChild(script)

  window.jsonp = function(data) {
    if(cb) cb(data)
    else document.querySelector('div').innerHTML = data;
  }
}

jsonp("http://127.0.0.1:3000/data.js", {pkg:123, chid:321})