Incoming links: React function component
@cirosantilli/_file/react/react/ref-click-counter-func.html Updated 2024-12-15 +Created 1970-01-01
Dummy example of using a React
ref This example is useless and to the end user seems functionally equivalent to react/hello.html.It does however serve as a good example of what react does that is useful: it provides a "clear" separation between state and render code (which becomes once again much less clear in React function components.
Notably, this example is insane because at:we are extracing state from some random HTML string rather than having a clean JavaScript variable containing that value.
<button onClick={() => {
elem.innerHTML = (parseInt(elem.innerHTML) + 1).toString()In this case we managed to get away with it, but this is in general not easy/possible.
Website: reactjs.org
React officially recommends that you use Next.js[ref], so just do it. It just sets up obvious missing functionality from raw React.
React feels like a good. But it also feels impossible to use/learn sometimes.
Its main design goal is to reduce DOM changes to improve rendering times.
And an important side effect of that is that it becomes easier to do stuff of the type:and then the new comment easily gets the callback attached to it.
- user creates a new comment that appears on screen without page reload
- comment has a delete button, which is JavaScript callback activated
And it also ends up naturally doubling as a template engine.
But React can also be extremely hard to use. It can be very hard to know what you can and cannot do sometimes, then you have to stop and try to understand how react works things better:The biggest problem is that it is hard to automatically detect such errors, but perhaps this is the same for other frontend stuff. Though when doing server-side rendering, the setup should really tell you about such errors, so you don't just discover them in production later on.
- cannot update a component while rendering a different component warning in React
- Rendered more hooks than during the previous render.
- cannot use hooks from helpers:
Is is also very difficult to understand precisely why hooks run a certain number of times.
Examples under: react.
- react/hello.html
- react/hello-func.html: Hello World with a React function component instead of classes. At page load console shows:and then after each click:
Mainso we understand thatonClick MainMaininsanely functions both as the constructor and as the render function in React function components. - react/hello-func-use-callback.html: same as react/hello-func.html but with useCallback. TODO no advantages in this case? When does it help?
- react/hello-without-jsx.html: Hello World in pure JavaScript, without JSX. Exactly equivalent to react/hello.html. Documented at: reactjs.org/docs/react-without-jsx.html Understanding this is fundamental to understanding React.
- react/prop-change.html: shows what gets called as parameters flow down through the tree.By looking at the console, we see all
renderget called every time, even ifpropsdidn't change, but not the constructors.After page load the console contains:Main.constructor Main.render NotMain.constructor NotMain.render NotMain2.constructor NotMain2.renderThen, every time we click the button it adds:handleClick Main.render NotMain.render NotMain2.renderNote how thepropsofNotMainonly change every other click, butrenderstill gets called every time.In order to makeReactnot re-render when there are not changes, you have to either:- define the
shouldComponentUpdatemethod of class components - wrap functional components in
React.memo
- define the
- react/prop-change-hook.html: same as react/prop-change.html, but using hooks. The notable difference is that functional components don't have a clear constructor/render separation, the function just gets called every time. Then React does some magic to ensure that
useStatereturns the current state, except for the first render where they return the initial value. - react/prop-change-hook-use-memo.html: TODO forgot if this example is useful, was tring to use
useMemo - react/prop-change-child.html: shows what child prop changes do not call render on parent,
Maindoes not show up on console when you click underNotMain - react/hook-from-function-fail.html: TODO got some errors that seemed linked to this on a larger program, but failed to minimize them here
- react/hook-different-number-of-times.html: this illustrates one of the cardinal points of using hooks: you must always call them the same number of times, otherwise it fails with:In the case of
React has detected a change in the order of Hooks called by Main. This will lead to bugs and errors if not fixed.
useState, we can kind of understand why this happens: React must use the order of calls to determine which state variable to return at each point in time. - react/hello-hook-use-effect.html: just checking when it gets called. Happens after every render
handleClick Main useEffect useEffect2 - TODO create a test
\a[react/img-broken.html]
How React works bibliography:
- www.netlify.com/blog/2019/03/11/deep-dive-how-do-react-hooks-really-work/ shows how
uesStateworks under the hood with crazy closures - medium.com/@gethylgeorge/how-virtual-dom-and-diffing-works-in-react-6fc805f9f84e
React function components do produce shorter code. But they are also impossible to understand without knowing what is their corresponding class component.
Hooks were introduced much after classes, and just require less code, so everyone is using them now instead of classes.