The WebWorker API provides a simple set of methods for web content to run scripts in background threads. Web workers are executed from a main browser window but run independently and in parallel. Once a script in the main thread spawns a worker, the worker can send messages back by posting them to a defined event handler. Data is serialized, not cloned, as it is passed back and forth. This is important to note because poor design or use of too many workers can actually cause performance issues.

Web workers are beneficial in that they run without impacting the other user interface scripts executed from the main window, but they do have limitations. They have limited access to core JavaScript, and no access to the Document Object Model (DOM).