Should I use React.PureComponent everywhere?

React says pure render can optimize performance. And now React has PureComponent. Should I use React.PureComponent everywhere? Or when to use React.PureComponent and where is the most proper postion to use React.PureComponent?

You should use it when a component could re-render even if it had the same props and state. An example of this is when a parent component had to re-render but the child component props and state didn't change. The child component could benefit from PureComponent because it really didn't need to re-render. You shouldn't necessarily use it everywhere. It doesn't make sense for every component to implement the shallow shouldComponentUpdate(). In many cases it adds the extra lifecycle method without getting you any wins.

It can drastically save you rendering time if you have many cases where root level components update while the children do not need to do so. That being said, you will gain much more from using PureComponent in your root level nodes (i.e. PureComponent will not improve overall performance as much in leaf level components because it only saves renders from that component).

Some caveats to PureComponent are explained very well in the react docs.

> React.PureComponent's shouldComponentUpdate() only shallowly compares the objects.

You could accidentally miss rendering updates if your prop changes are deep in a nested object. PureComponent is only great with simple flat objects/props or by using something like ImmutableJS to detect changes in any object with a simple comparison.

> Furthermore, React.PureComponent's shouldComponentUpdate() skips prop updates for the whole component subtree. Make sure all the children components are also "pure".

PureComponent only works whenever the rendering of your component depends only on props and state. This should always be the case in react but there are some examples where you need to re-render outside of the normal react lifecycle. In order for PureComponent to work as expected (skipping the re-rendering you don't really need to happen), every descendant of your PureComponent should be 'pure' (dependent only upon props and state).

According to this reference, no (you should not use it everywhere):

> (I work on React.) [...] If we recommended that PureComponent be used everywhere, it would probably be the default already. Rather -- the comparison to decide whether or not a component should be rerendered costs something, and in the case that you do want to rerender, all of the time spent checking whether you should have rerendered is wasted. > > Instead, we'd suggest you be conscious of where you need to do the comparisons. It's usually only in a couple of places in your app. Good candidates are on the children of a long list or around large parts of the app that change independently (that is, cases where you know the parent should often rerender but the child shouldn't). A few well-placed shouldComponentUpdate (or PureComponent) uses can go a long way.

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I found a tweet from Dan Abramov saying the same thing (30 Jul 2016).