Promise constructor

promise_constructor.js

function getSomeJSON(url, callback) {
  // AJAX call to get data from server. Accepts callback and calls
  // with callback(err, response)
  ...
}
  
function fetchJSON(url) {
  return new Promise(function (resolve, reject) {
    getSomeJSON(url, function (err, response) {
      if (err) return reject(err);
      resolve(response);
    });
  });
}
  
fetchJSON("http://www.google.com").then(..);