Save-Data header service worker

save-data-header.js

"use strict";

this.addEventListener('fetch', event => {

// Save Data support
if(event.request.headers.get('save-data')){
    //Return smaller images
    if (/\.jpg$|.gif$|.png$/.test(event.request.url)) {

      let saveDataUrl = event.request.url.substr(0, event.request.url.lastIndexOf(".")) + '-savedata' + event.request.url.substr(event.request.url.lastIndexOf("."), event.request.url.length - 1);

      event.respondWith(
        fetch(saveDataUrl, {
          mode: 'no-cors'
        })
      );
    }

    // We want to save data, so restrict icons and fonts too
    if (event.request.url.includes('fonts.googleapis.com')) {
        // return nothing
        event.respondWith(new Response('', {status: 408, statusText: 'Ignore fonts to save data.' }));
    }
  }

});