300ms Faster: Reducing Wikipedia's total blocking time

TBT measures the sum of the blocking portion of all long tasks on the browser's main thread between First Contentful Paint and Time to Interactive. The "Blocking portion" is the time after 50ms of each long task. The 80ms task is 30ms longer than 50ms so contributes 30ms to TBT. The 30ms task doesn't contribute to TBT since it is less than 50ms and NOT a long task. The 100ms task is 50ms longer than 50ms so contributes 50ms to TBT. Since TBT is the sum of the time exceeding 50ms of each long task, the TBT for this example is 30ms + 50ms = 80ms. When tested on average mobile hardware, Google recommends sites have a TBT of less than 200 milliseconds. Wikipedia had one task that could take over 600 milliseconds - roughly 3x the recommended TBT limit for this one task alone. Overall, these two steps reduced TBT by nearly 300ms on devices like the Moto G phone visiting long articles. To achieve even greater reductions in TBT, it may be necessary to break up the task into smaller tasks.