C H A P T E R  10

Using the Web Workers API

JavaScript is single-threaded. As a result, long-lasting computations (not necessarily due to poorly written code) will block the UI thread and make it impossible to add text to text boxes, click buttons, use CSS effects, and, in most browsers, open new tabs until control has returned. As an answer to that problem, HTML5 Web Workers provide background-processing capabilities to web applications and typically run on separate threads so that JavaScript applications using Web Workers can take advantage of multicore CPUs. Separating long-running tasks into Web Workers also avoids the dreaded slow-script warnings, shown in Figure 10-1, that display when JavaScript loops continue for several seconds.