Async is short for asynchronous and refers to the process of loading individually the resources of a web page. Let’s break this concept down.
A resource is every item included in a web page: Images, text (HTML pages), cascading style sheets (CCS), they are all resources. For users to see the web page as it was designed and enjoy all the features and functionalities, the resources must be totally downloaded. In the past, every resource downloaded sequentially, which means that one resource had to be downloaded entirely for the second to start downloading, and so on.
It worked perfectly for those early years on the web. However, things have slightly changed ever since. Nowadays, businesses depend significantly on SEO to succeed in the online world. In other words, they must provide customers with a great user experience to achieve the highest ranking possible in the search engine result pages.
One of the main aspects of good user experience is the loading speed of a website. That is when asynchronous resources enter.
Each page can have a different amount of resources. The more resources within a web page, the heavier it is to load.
One technique to speed up the load process is by using asynchronous resource loading. It means loading every resource individually. It will surely help users see and use the page faster. But remember that users are not the only ones browsing your website, so are web crawlers.
Bots, also known as web crawlers, are responsible for the analysis of your website to decide if it is appropriately optimized. They have a massive impact on your website ranking. So, it is crucial that they receive the same information as your users. Make sure your web pages are equally fast to download for end users and for web crawlers to ensure a higher ranking.