Open https://fast.com/ and paste into the console to start creating a log of your internet speed.

speed_tracker.js

const recordedSpeeds = []
setInterval(() => {
  // Get internet speed
  let speed = document.getElementById('speed-value').innerText
  // Get speed units
  const units = document.getElementById('speed-units').innerText
  // Flatten speed if Kbps
  if (units === 'Kbps') speed = "0"
  // Display in console
  console.log('='.repeat(Number(speed) / 5), speed)
  // Save to array of internet speeds
  recordedSpeeds[Date.now()] = speed
  // Run the speed test again
  document.getElementById('speed-progress-indicator').click()
}, 60000) // 1 minute

// Example output:
// ======== 42
// =========== 59
// ========= 47
// ========== 51
// ========== 53