For a better performance, it is recommended to increases the amount of Web Workers. This will enable the javascript engine to utilize multiple cores on your cpu. Any amount above your actual amount of CPU threads will have no effect.
You can see the full project on github at cloutierMat/interactable-mandelbrot.git
A Mandelbrot set animation create in javascript only, using the canvas. I also take advantage of webworkers to improve computational performance.