Counting byte savings using Server-Timing

total-bytes-saved.js

window.addEventListener('load', function() {
  let totalBytesSaved = 0
  for (const {encodedBodySize, serverTiming} of performance.getEntriesByType('resource')) {
    for (const {name, description} of serverTiming || []) {
      if (name === 'disk') {
        totalBytesSaved += parseInt(description) - encodedBodySize
      }
    }
  }
  console.info('Total Bytes Saved:', totalBytesSaved)
})