7. Competition

JavaScript is single-threaded and non-preemptive. These words mean that the evaluator does only one thing at a time and does only that thing until it is completed. There are two major consequences:

• Each execution can be considered critical since nothing can prevent it from being carried out.

• An infinite loop will therefore never end.

On the other hand, the primitive JavaScript runtime library (for example, the one provided by browsers) knows how to perform actions in parallel, such as fetching pages, images, and scripts, and processing them appropriately once their content has been obtained. Communication between these two worlds takes place via events and callbacks. The term callback can also be translated as "return function," but this is less concise than "continuation,"...