High Performance Mobile Web

Chapter 3. Web Performance Basics

When learning to measure web performance, one of the first goals we need to achieve is understanding the metrics and vocabulary.

Measuring techniques will allow us to get accurate information about our current status, to define goals to achieve, and to measure again to see whether applying a technique improves performance or not.

In this chapter, you will learn about the web performance optimization vocabulary and metrics, so you understand how to analyze your improvements.

We need to remember that measuring is a critical part of improving performance. After all:

If you can’t measure it, you can’t improve it.

Peter Drucker

We will organize performance measurements into two big categories: loading and responsiveness.

Loading Measurement Basics

For years, web performance was defined by two measurements: the window’s onload event and the time that the server was taking to send the response. Today, we know that these units are not so important in terms of web performance, as they don’t focus on the most important factor here: the user’s perception.

We’ll define loading performance as the measures that define how fast your website or web content appears on the user’s screen, including fetching the resources and rendering those resources on the screen. We will see that the “perceived performance”—that is, how fast the user perceives the site to be—is often more important than the actual total load time. This is determined by the moment when a user ...