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How prefetching helped Terra enhance advertisements click-through fee by 30% and velocity up Largest Contentful Paint.

Prefetching is a method used to hurry up web page loading by downloading sources—and even total pages—that are prone to be wanted within the close to future. Analysis has proven that quicker load instances end in larger conversion charges and higher consumer experiences.

Terra is without doubt one of the largest content material portals from Brazil, providing leisure, information, and sports activities with greater than 63 million distinctive guests monthly. We’ve collaborated with Terra’s engineering workforce to enhance the loading time of articles through the use of prefetching methods on sure sections of their web site.

This case research describes Terra’s journey implementation which resulted in a 11% advertisements click-through fee (CTR) enhance on cell, 30% advertisements CTR on desktop, and 50% discount within the Largest Contentful Paint (LCP) instances.

Prefetching technique #

Prefetching has been round for some time, however you will need to use it rigorously because it consumes additional bandwidth for sources that aren’t instantly vital. This system ought to be utilized thoughtfully to keep away from pointless information utilization. Within the case of Terra, articles are prefetched if the next circumstances are met:

  • Visibility of hyperlinks to prefetched articles: Terra used the Intersection Observer API to detect viewability of the part containing the articles that they needed to prefetch.
  • Favorable circumstances for elevated information utilization: As talked about beforehand, prefetching is a speculative efficiency enchancment that consumes additional information, and that will not be a fascinating end result in each state of affairs. To scale back the probability of losing bandwidth, Terra makes use of the Community Info API together with the Machine Reminiscence API to find out whether or not to fetch the subsequent article. Terra solely fetches the subsequent article when:
    • The connection velocity is at the least 3G and the system has at the least 4GB of reminiscence,
    • or if the system is operating iOS.
  • CPU idle: Lastly, Terra checks if the CPU is idle and capable of carry out additional work through the use of requestIdleCallback, which takes a callback to be processed when the principle thread is idle, or by a particular (non-compulsory) deadline—whichever comes first.

Adhering to those circumstances ensures that Terra solely fetches information when vital, which saves bandwidth and battery life, and minimizes the affect of prefetches that find yourself going unused.

When these circumstances are met, Terra prefetches the articles current within the sections: “Associated Content material” and “Really helpful for you” highlighted in blue beneath.

A screenshot of the two sections on the Terra website in which links were prefetched. At left, the 'Related content' section is highlighted, whereas on the right, the 'Recommended for you' section is highlighted.

Enterprise Influence #

With the intention to measure the affect of this method, Terra first launched this characteristic within the “Associated content material” part of the article web page. A UTM code helped them to distinguish between prefetched and non-prefetched articles for comparability functions. After two weeks of profitable A/B testing, Terra determined so as to add the prefetching performance to the “Really helpful for you” part.

Because of prefetching articles, an general enhance of advertisements metrics and a discount of LCP and Time to First Byte (TTFB) instances have been noticed:

Prefetching—when used with care—vastly improves web page load time, will increase advertisements metrics, and reduces LCP time.

Technical particulars #

Prefetching will be achieved via the usage of useful resource hints corresponding to rel=prefetch or rel=preload, by way of libraries corresponding to quicklink or Guess.js, or utilizing the newer Hypothesis Guidelines API. Terra has chosen to implement this through the use of the fetch API with a low precedence together with an Intersection Observer occasion. Terra made this alternative because it permits them to assist Safari, which does not but assist different prefetching strategies like rel=prefetch or the Hypothesis Guidelines API, and a full-featured JavaScript library wasn’t vital for Terra’s wants.

The beneath JavaScript is roughly equal to the code utilized by Terra:

operate prefetch(nodeLists) {
// Exclude sluggish ECTs
if (navigator.connection &&
(navigator.connection.effectiveType === 'slow-2g'
|| navigator.connection.effectiveType === '2g')
) {

// Exclude low finish system which is system with reminiscence
if (navigator.deviceMemory && navigator.deviceMemory 2) {

const fetchLinkList = {};

const observer = new IntersectionObserver(operate (entries) {
entries.forEach(operate (entry) {
if (entry.isIntersecting) {
if (!fetchLinkList[]) {
fetchLinkList[] = true;

fetch(entry.goal, {
precedence: 'low'

observer.unobserve(entry = entry.goal);

const idleCallback = window.requestIdleCallback || operate (cb) {
let begin =;

return setTimeout(operate () {
didTimeout: false,
timeRemaining: operate () {
return Math.max(0, 50 - ( - begin));
}, 1);

idleCallback(operate () {

  • The prefetch operate first checks for a minimal connection high quality and system reminiscence earlier than initiating prefetching.
  • Then it makes use of an IntersectionObserver to observe when components grow to be seen within the viewport, and subsequently provides URLs to an inventory for prefetching.
  • The prefetch course of is scheduled with requestIdleCallback, aiming to execute the prefetch operate when the principle thread is idle.

Conclusion #

When used with care, prefetching can considerably scale back load instances for future navigation requests, thereby decreasing friction within the consumer journey and rising engagement. Prefetching leads to loading of additional bytes that will not be used, so Terra took additional steps to solely prefetch below good community circumstances and on succesful gadgets, the place this info is accessible.

Particular due to Gilberto Cocchi, Harry Theodoulou, Miguel Carlos Martínez Díaz, Barry Pollard, Jeremy Wagner, and Leonardo Bellini and Lucca Paradeda from Terra’s Engineering workforce for his or her contribution to this work.



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