Web browsers have several major components, including the rendering engine (the part that displays web pages) and JavaScript engine (the part that runs scripts in pages). V8 was created alongside Chrome, and is used in many other browsers and runtimes based on the Chrome codebase.

Earlier today, the V8 team shared some details about improving the engine's performance over the past year. Traditionally, benchmarks like Octane have been used to measure the peak performance of a JavaScript engine. The results showed what the V8 engine was capable of, but it didn't accurately reflect real-world performance (just like Android benchmarks don't always show how fast a phone is in daily use).

So the V8 team began testing the engine on popular websites, including Facebook, Reddit, Twitter, and Wikipedia. A new 'Speedometer' benchmark was created that tests commonly-used JavaScript libraries. The Speedometer results revealed that typical web pages rely more on 'startup' performance, or how long it takes to start running scripts. So over the past year, several optimizations were implemented that resulted in 10-20% faster load times (depending on the CPU architecture).

Of course, Chrome has added some other performance optimizations unrelated to the V8 engine over the past year. Video loading has been much improved, most background tabs are now throttled, and GPU-intensive features run faster.

Source: Chromium Blog