Asynchronism

In general, there are two ways / paradigms asynchronism can be done.

Async #1 : Pre-computing

Referring to a web app this means doing the time-consuming work in advance and serving the finished work with a low request time.

Very often this paradigm is used to turn dynamic content into static content. Pages of a website, maybe built with a massive framework or CMS, are pre-rendered and locally stored as static HTML files on every change. Often these computing tasks are done on a regular basis, maybe by a script which is called every hour.

This pre-computing of overall general data can extremely improve websites and web apps and makes them very scalable and performant. Just imagine the scalability of your website if the script would upload these pre-rendered HTML pages to AWS S3 or Cloudfront or another Content Delivery Network! Your website would be super responsive and could handle millions of visitors per hour!

Async #2 : Handle tasks asynchronously

Here is a typical workflow:

A user comes to your website and starts a very computing intensive task which would take several minutes to finish. So the frontend of your website sends a job onto a job queue and immediately signals back to the user: your job is in work, please continue to the browse the page. The job queue is constantly checked by a bunch of workers for new jobs. If there is a new job then the worker does the job and after some minutes sends a signal that the job was done. The frontend, which constantly checks for new “job is done” - signals, sees that the job was done and informs the user about it. I know, that was a very simplified example.