jsonp.js

(function () {
  var _id = 0
  
  window.jsonp = function (url, callback) {
    var id = 'jsonp_cb_' + _id,
        existing = document.scripts[0],
        script = document.createElement('script')
  
    window[id] = function (data) {
      script.parentNode.removeChild(script)
      callback(data)
      delete window[id]
    }
  
    script.src = url + (~url.indexOf('?') ? '&' : '?') + 'callback=' + id
    existing.parentNode.insertBefore(script, existing)
    _id += 1
  }
}())