creates a binder session on the background

fetch_binder.js

fetch = function() {
  // URL of the repository
  var apiUrl = 'https://notebooks.gesis.org/binder/build/gh/gesiscss/smm_demo/master';
  
  eventSource = new EventSource(apiUrl);
  eventSource.onerror = function(err) {
    console.error("Failed to construct event stream", err);
  };
  
  eventSource.addEventListener("message", function(event) {
    var data = JSON.parse(event.data);
    if (data.phase == 'ready') {
      // data['url'] and data['token'] are both required to assemble the URL      
      console.log(data['url'] + '?token=' + data['token']);
      eventSource.close();
    }
  });
};