Cookies are used on a lot of websites - 83.9% of the 5.7 million home pages tracked in the HTTP Archive to be specific. They are essentially a name/value pair set by a server and stored in a client’s browser. Sites can store these cookies by using the
document.cookie). On subsequent requests, these cookies are sent to the server in a
Cookie HTTP request header.
Why it occurs, and what is the impact on web performance?
Last year Google announced updates to Chrome that provide a way for developers to control how cross site cookies should work on their sites. This is a good change - as it ultimately improves end user security and privacy by limiting which third parties can read cookies that were set while visiting a different site. It also defeats cross site request forgery attacks. The implementation is fairly simple, and only requires developers to add the SameSite attribute to their cookies.
Back in 2017 the maximum validity lifetime for an HTTPS certificate was set to 825 days, a decision that was widely supported by both browsers and certificate authorities. However, since then there have been multiple unsuccessful attempts at reducing the maximum lifetime to one year. Scott Helme has written about this previously, and his blog post noted that browser vendors unanimously supported this while some certificate authorities objected to it.
According to the HTTP Archive, 84% of HTTPS certificates are using the Subject Alternate Name (SAN) extension, which allows multiple hostnames to be protected by a single certificate. The largest certificate I found in the HTTP Archive contained a whopping 1275 alt-names! During this post we’ll explore why this is a web performance problem, and how you can determine what a reasonable limit would be for your certificates.
Earlier this year the Chrome team announced plans to support lazy loading natively in the browser. The plan was to add a loading attribute in both
<iframe> elements. Chrome 75 included it behind a feature flag so that developers could test it out. Last week, with the release of Chrome 76 this feature became generally available. I was surprised to see that it is already in use by more than 1000 sites. Lazy loading is an easy web performance win, so you may want to try this out on your sites.
console.log() to print messages for debugging purposes. For example:
When we talk about cacheability of web content, often times the discussion is around content that site operators have control over (ie, first party content). But what about third party content? How much of that is cacheable? I was chatting with @yoav about this on Friday, since it could be useful to understanding the benefits of signed exchanges on accelerating third party content. Is it worth delivering cross origin resources on a site’s HTTP/2 connection, avoiding the need to establish a new connection and eliminate bandwidth contention between 3rd party resources and 1st party ones? In order to answer that we need to understand how many third party resources are delivered without credentials, and therefore can be signed. We will use the resource’s public cacheability as a proxy for that, and try to understand how common such third party resources are.