SSE API to see when cache is updated

[dpwspoon]

Possible options

Before (A) - schedule repeating XHRs at fixed interval

var sendXHR = function(...)
{
  var xhr = new XMLHttpRequest();
  ...
  xhr.send("");
};
window.setInterval(sendXHR, 30)

Before (B) - chain next XHR after previous XHR

var sendXHR = function(...)
{
  var xhr = new XMLHttpRequest();
  ...
  xhr.send("");
  xhr.onload = function() { ...; setTimeout(sendXHR, 30); };
};

After (1)

var sendXHR = function(...)
{
  var xhr = new XMLHttpRequest();
  ...
  xhr.oncachechanged = sendXHR;  
  xhr.send("");
};

After (2) - defers response when previous answer already known

var sendXHR = function(...)
{
  var xhr = new XMLHttpRequest();
  ...
  xhr.setRequestHeader("Prefer", "wait=30"); // RFC 7240
  xhr.send("");
  xhr.onload = function() { ...; sendXHR(...); };
};

[hthetiot]

Possible progress event use case. Source: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/responseType