React Render Tutorial – 15 – Context and memo
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Video Title: React Render Tutorial – 15 – Context and memo
In the last video we learned about the rendering behavior with respect to the context api we learned that when the context provider is in the parent component and the parent components state updates every child component re-renders and not just the component consuming the context value
In this video let’s see what is a simple possible solution to improve the rendering behavior right now in our example when the count state updates the default rendering behavior causes all the children components to re-render ideally what we want is only the parent component and the child c component to read enter
The way to achieve that is using react memo in the contextchildren.js file apart from exporting child a i’m also going to export my moist child a so export const memoized child a is equal to react dot memo and we pass in child a component and back in the parent component we are
Going to import memoized child a and use that as a child of the context provider let’s now head to the browser and test this out on page load we have the four log messages corresponding to the initial render now if i clear the console and click on the count
Button we see the log messages from only the parent and child c component the rendering behavior is optimized to the way we want it to behave let’s quickly understand what is happening here when we click on the count button the state changes in the parent component which causes the parent component to re-render
Because the parent rendered react now has to re-render the child component for the child component is wrapped with react memo so react checks if the props have changed since there are no props to begin with props haven’t changed and react decides it doesn’t have to render the child a component
Since the child a component did not render child b component has no reason to render so we don’t see the log statements for child a and child b now react arrives at child c it sees that it consumes the count context value whose value has now changed so react proceeds to
Re-render child c component so any time we increment the count value and provide a new value to the context provider only the component consuming that value is re-rendered in our case that is the child c component now something you have to remember is that if the child c component has children components
Those children components will get re-rendered because of the default parent child rendering behavior in react but this is pretty much how you can optimize the context rendering behavior with react memo by wrapping the child component of the context provider with react memo state updates in the parent component
Will not force every component to re-render but only the components where the context is consumed in the next video let’s see another technique to optimize context rendering behavior
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Hello sir. I have a question. As memoizedChildA is not rendered, consequently childB also not rendered. So obviously childC shouldn't get rendered as childB didn't render. But we saw childC got rendered! can you explain this sir..
VERY NICE!
ty.
Hii..sir .,this is tejasri ..4yr cse studied ..I learning react from 2 month through your video.. I gain knowledge of fundamental..advance and hook in react ..In my collage mini project wave is running.. I want suggestion from you about a reactjs based project idea for beginner to apply in her mini project..