So you heard React was fast, and decided to give it a go. You grabbed a boilerplate, started working through it, and noticed
PureRenderMixin. Some googling reveals these are the things you use to make React fast. But wasn’t React already fast?
The answer is that React is fast… sometimes. The other times, you should use
shouldComponentUpdate. But when are the other times? Wouldn’t it be so much easier if there was just a simple yes-no question which you could ask to decide whether to use
shouldComponentUpdate or not? And wouldn’t you believe it, there is!