Can Service Workers respond to synchronous XHR requests?

Question

I would like to use Service Workers to enhance an existing web site. In particular, I would like to add better offline support by having Service Workers respond to requests

Answer 1

You could create a synchronous effect by chaining asynchronous calls together. It creates indented callbacks - whereas promises would make the code easier to read - but the 2nd Ajax call won't be made until after the 1st one has returned. Note that the 3rd parameter is set to true in both calls.

// Synchronized Ajax calls using 2 nested Asynchronous calls

// Asynchronous request #1 using traditional API
const axhr = new XMLHttpRequest();
axhr.open('GET', '/__so-example__', true);
axhr.onload = event => {
  console.log("A-XHR: " + axhr.responseText);

  // Asynchronous request #2 using traditional API
  const sxhr = new XMLHttpRequest();
  sxhr.open('GET', '/__so-example__', true);
  sxhr.onload = event => {
    console.log("S-XHR: " + sxhr.responseText);
  }
  sxhr.send();
}
axhr.send();

It's just an example. I assume that promises could be chained just as easily (but vertically stacked, instead of right indented) to create a synchronous effect.