To help focus our attention on CPU, several new performance metrics have been defined and evangelized over the last year or three. In this post I'm going to focus on these:
Here's a figure to help visualize these metrics.
<link rel="preload" href="main.js" as="script">
This blog post has a simple conclusion: Load script asynchronously! Simple, and yet the reality is that most scripts are still loaded synchronously. Understanding the importance of loading scripts asynchronously might help increase adoption of this critical performance improvement, so we're going to walk through the evolution of async script loading starting way back in 2007. Here's what loading 14 scripts looked like in Internet Explorer 7:
The number of performance metrics is large and increases every year. It's important to understand what the different metrics represent and pick metrics that are important for your site. Our Evaluating rendering metrics post was a popular (and fun) way to compare and choose rendering metrics. Recently I created this timeline of performance metric medians from the HTTP Archive for the world's top ~1.3 million sites:
When looking to improve the performance and user experience of our sites we often start by looking at the network:
What's the time to first byte?
How many requests are we making and how long are they taking?
What's blocking the browser from rendering my precious pixels?
While these are entirely valid questions, over the last few years we've seen a growing number of web performance issues that are caused, not by the network, but by the browser's main thread getting clogged up by excessive CPU usage.
We're excited to announce the availability of the First Input Delay metric as part of LUX, SpeedCurve's RUM product.