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okay, let's dive deep into what causes react components to re-render, why it matters, and how to optimize it. we'll cover various scenarios, with code examples and explanations.

*why re-renders matter in react*

react's component-based architecture thrives on the concept of state and props. when these change, react intelligently updates the ui by re-rendering components. however, unnecessary re-renders can lead to:

1. *performance degradation:* frequent re-renders, especially in complex components or with large data sets, can slow down your application, leading to a sluggish user experience. the browser has to do more work to update the dom.
2. *increased cpu usage:* excessive rendering consumes more cpu resources, which can be problematic on low-powered devices or when dealing with computationally intensive components.
3. *unintended side effects:* if you have side effects within your component's render function (e.g., making api calls, updating external libraries), unnecessary re-renders can trigger these side effects multiple times, causing unexpected behavior.
4. *wasted resources:* even if the visual output is the same, react still has to perform the calculations to determine if the component needs updating, which is a waste of resources.

*core concepts*

before we get into the nitty-gritty, let's define some key terms:

*component:* a self-contained, reusable piece of ui.
*state:* data that is private and fully controlled by the component itself. changing state triggers re-renders.
*props:* data passed from a parent component to a child component. changing props triggers re-renders.
*virtual dom:* react's internal representation of the ui. when state or props change, react compares the new virtual dom with the previous one and applies only the necessary changes to the actual dom.
*render function:* the function within a react component that returns the jsx (or react elements) that define the ui.
* ...

#React #ReRender #codingmistakes
React components
re-rendering
state changes
props updates
useEffect
component lifecycle
performance optimization
memoization
React hooks
virtual DOM
key prop
shallow comparison
PureComponent
functional components
conditional rendering