React.Component doesn’t implement shouldComponentUpdate?

Question

According to the docs, React.Component doesn't implement shouldComponentUpdate ?

So how about a lifecycle of a component (the-component-lifecycle) (shouldcomponentupdate) ?

React.PureComponent is similar to React.Component. The difference between them is that React.Component doesn’t implement shouldComponentUpdate(), but React.PureComponent implements it with a shallow prop and state comparison.

@DanielReina As you can see, in one part of the docs, they say that React.Component doesn't implements shouldComponentUpdate function, which seem not to be true, accroding to the other part of the docs. — Src
– Src, Commented Jan 15, 2018 at 22:05

Geraint · Accepted Answer · 2018-01-15 22:42:47Z

2

By default, using Component, shouldComponentUpdate returns true (no diffing of props happens), unless its defined by you (result dependent of what you put in). Using PureComponent react does a shallow diff of props by default.

Feel free to take a look at the react source code, roughly, it checks if shouldComponentUpdate is defined and is a function. Then checks if it is a pure component, then returns true by default.

https://github.com/facebook/react/blob/master/packages/react-reconciler/src/ReactFiberClassComponent.js

edited Jan 15, 2018 at 22:42

answered Jan 15, 2018 at 22:09

Geraint

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4 Comments

Src Over a year ago

So, when we're extending Component class, react doesn't perform any checks and always re-renders whole component -_-?

Geraint Over a year ago

Correct, if you look at the react source code github.com/facebook/react/blob/master/packages/react-reconciler/… line 157 checkShouldComponentUpdate

Src Over a year ago

In every tutorial, first thing to mention is always react shadow DOM and the fact, that react always update only necessary part of the component. So, accoring to everything you wrote above, it's not true? Or maybe i'm missing something?

Geraint Over a year ago

I see your point, I might be wrong on this one...but just because it should update it doesn't mean it will update

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