I'm looking at the video https://youtu.be/uirRaVjRsf4. Apologies, there is no code for this, so I just captured the screen.
What I don't understand is when is the class Counter instantiated ? Usually in a program, I need to create the instance by calling Counter(xxxx). But in this react program, I cannot find the code to instantiate the object.
Thanks.
Class not a necessary instance when rendering component, but it is a short answer, but in some cases react engine preload class component in virtual DOM implementations and use shallow access to them. Because of this pattern, things like class stateful are not recommended these days because this keyword has been bound for virtual DOM and some unexpected behavior came from.
It would help if you read about component lifecycle to figure out how this "magic" works
Related
Hooks, as I understand them, are just a way to add state (and lifecycle methods) to function components.
This FAQ answer:
In the longer term, we expect Hooks to be the primary way people write React components.
https://reactjs.org/docs/hooks-faq.html#should-i-use-hooks-classes-or-a-mix-of-both
and this documentation snippet:
Hooks let you split one component into smaller functions based on what pieces are related
https://reactjs.org/docs/hooks-intro.html
confuse me slightly as a React beginner.
It is as if I have to think about my app in terms of hooks rather than in terms of elements and components.
React didn't remove components, but the quote hints that hooks will replace
components as the primary source of code reuse.
Can one still talk about elements and components as primary abstractions in React?
The concept of components is not going away, it's just how they are written that is changing.
The second line you quoted
Hooks let you split one component into smaller functions based on what pieces are related
Is poorly worded in my opinion, and should rather say "Hooks let you split one class component into smaller functional components..."
So instead of having one monolithic class that handles all state and lifecycle logic in methods like componentDidMount, componentDidUpdate, you can split areas of concern and have smaller functional components that only care about things directly related to themselves.
Edit: This snippet from the hooks-intro doc might be helpful:
Hooks don’t replace your knowledge of React concepts. Instead, Hooks provide a more direct API to the React concepts you already know: props, state, context, refs, and lifecycle. As we will show later, Hooks also offer a new powerful way to combine them.
Currently, there are 2 ways of building components in React:
Class Component
Functional Component
You can check them here. The way you build it it's different. In case you approach the class component, that means that you need to work with the prototype of the object.
On the other side, if you choose to go as a functional component, that means that everything you request from React, is invoking a function, and not using the prototype at all. All this chaining from JS can slow down the performance, and that's why the React core team decided to go into pure functional direction: It can perform better, and it makes it even simpler to read it (once you get used to it).
Regarding the second quotation. It is a way to show more benefits of functional programming over classes. They are more flexible and can have a better composition for it.
One last addition: Approaching functional components doesn't mean you can ignore to learn class components. There's still a lot of apps with some legacy code. I would recommend learning both, and whenever you need to create new components, approach the functional component paradigm.
I am learning about the somewhat newly introduced React.Context API, but I've noticed some inconsistencies on it's consumption across examples. Some use the original Context.Consumer HOC method, while some (including the React Docs) use the static Class.contextType method.
What's the difference and why the inconsistency?
Turns out that the static Class.contextType was newly introduced on React v16.6.0, as the Context.Consumer method proved problematic on class components. Also, there does seem to be one major difference between using both, and it's that the static Class.Context only allows you to subscribe to a single context.
The good news is that both of them seem to reliably listen of Context changes which means if you only have a single Context API, then both are good enough.
Stack: Meteor, React, Redux, React Router
Question: Where (i.e. in which file) do I instantiate Globalize? I am no expert on Globalize, but it feels like this is a somewhat global variable. So where does it go?
More generally speaking I am a bit confused as to where to put global variables in react/meteor applications. I get the whole component idea. And I write a component within its module, I import all the stuff I need and I export the component. Easy enough. However, where does the more general stuff go? Is there anything I could read up on?
Cheers
I'm starting a new React app and, seeing all the news in the ecosystem, I want to go slow and actually consider my choices, starting with just React/Webpack/Babel, and introducing more.
The first of these choices is whether to use Flux or not (more precisely, Redux, which looks great and seems to have won the flux wars). Here is where I am:
I understand Redux's benefits, summarized on SO by Dan Abramov. They look great, but I'd rather introduce things one step at a time.
In plain React, parent→child communication is done with props, and child→parent communication happens with callbacks. See Doc / Communicate Between Components, or SO / Child to parent communication in React (JSX) without flux, or this codeacademy Redux tutorial which starts out by saying "no need for Redux if you're fine with plain React and all your data in a root component".
Which looks just fine for my purpose...
... however, the sad part is that these callbacks have to be passed down the component chain, which becomes quickly tedious as the levels of nesting grow.
To solve this without introducing new dependencies, I found two articles (1: Andrew Farmer, 2: Hao Chuan) encouraging usage of the recently-introduced context feature of React.
→ Using context would let me expose my model-mutating callbacks to my child components. To me it doesn't sound like a horrible misuse: I wouldn't be passing model data, just references to functions for binding on event handlers.
Does it sound sane?
Any other plain-React suggestion for convenient child→parent communication?
Thanks.
Answering my own question after watching Dan Abramov's Getting Started with Redux series, which I warmly recommend.
Yes it looks like it's sane: Redux faced the very same problem and solved it with Context (at least initially, the implementation may have changed). It is implemented and packaged (among other things) in the react-redux bindings under the <Provider> component and the connect() function.
Initially, at the start of step 24 - Passing the Store Down Explicitly via Props , we have a Todo app with a Redux store available as top-level variable. This sucks (for 1. testability/mockability, 2. server rendering needing "a different store instance for every request because different requests have different data"), so the store is demoted from top-level variable to a root component prop.
As in my case, having to pass the store as prop to each component is annoying, so in 25 - Passing the Store Down Implicitly via Context, Dan demonstrates using Context to pass the Redux store to arbitrarily nested components.
It is followed by 26 - Passing the Store Down with <Provider> from react-redux, explaining how this was encapsulated in the react-redux bindings.
And 27 - Generating Containers with connect() from React Redux further encapsulates generation of a container component from a presentational component.
Personally, I find the question quite simple to answer, if you think about the way dependency injection in Angular works. In Angular you have your DOM, and then you have all those services, providers, factories, constants and whatnot, which are independent of the DOM structure and can be imported simply by mentioning their name when creating modules or controllers.
I liken the use of this.context to DI. The difference w.r.t to Angular is that instead of stating the dependencies using function parameter names, you use childContextTypes and instead of getting the dependencies as function arguments, you get them through this.context.
In this sense, asking the question whether passing model mutators through this.context is sane, boils down to whether it makes sense in Angular to register your model for dependency injection. I've never seen a problem with the latter, therefore I deduce that the former is also quite OK.
I'm not saying that it suits the spirit of the library, though. Dependency injection and in particular managing dependencies between injected component is not as explicit, so one may argue that it's not the React way. I leave this philosophical discussion to others.
Tons of examples, describing React and Flux uses global variables: global Dispatcher, global Store and etc. Is there any way to proper inject dependencies to react components? There are some articles on the web describing how to use Dependency Injection component with React, but it based on undocumented weird feature called "Context" with unknown future.
Proper injection, for me, is classic constructor-based injection, without accessing global variables, without accessing static state and other.
It seems that I need to hook into component construction process (place, where new called). Can I do that? If so, how can I do that?
The most straightforward way to do dependency inversion with React is to simply pass any necessary dependencies as properties to the components that need them. Context is simply a way to pass the props down through child components, grandchild components, and so on implicitly without listing the prop on every component that may need it.
You'll find a lot of examples of this technique in the wild, and many make use of context and other niceties. React Redux is a popular one right now; pass a local variable to a top-level <Provider> component as a property, and it wires up the rest for you.
Dependency injection is less straightforward, and you'd probably need some kind of proper DI container or a DI library for JavaScript to do this nicely. Components aren't really instantiated, from the user's standpoint, the way other JS objects are, so doing "at instantiation time" injection of dependencies into components isn't how I'd approach the problem.