I just checked out HOC's in React. They are pretty cool. However, doesn't simply wrapping a component achieve the same result?
Higher Order Component
This simple HOC passes state as properties to the ComposedComponent
const HOC = ComposedComponent => class extends React.Component {
... lifecycle, state, etc;...
render() {
return (<ComposedComponent {...this.state} />);
}
}
Component Wrapping
This component passes state as properties to the child component
class ParentComponent extends React.Component {
... lifecycle, state, etc;...
render() {
return (
<div>
{React.cloneElement(this.props.children, { ...this.state })}
</div>
);
}
}
Although usage is slightly different between the two, they both seem to be equally as reusable.
Where is the real difference between HOC's and composing components via this.props.children? Are there examples where you can only use one or the other? It is a better practice to use HOC's. Are these just choices that you have where you get to pick your preferred flavor?
Higher-Order Components (HOC) and Container Components are different. They have different use cases and solve similar, but different problems.
HOC are like mixins. They are used to compose functionality that the decorated component is aware of. This is opposed to Container Components that wrap children and allow the children to be dumb (or not aware of the Container's decorated functionality).
It is true when transferring props, that Containers can add functionality to their children. But, this is usually in the form of props being passed down to the children. In Containers, this is also awkward because of the limitation that you cannot simply add props to an already created Element:
So, if you wanted to add a new prop to a child from this.props.children, you would have to use cloneElement. This is not as efficient because it means you have to re-create the elements.
Also, HOC is simply a way (factory) for creating Components. So, this can happen outside the render.
I just wanted to add that when you need to dynamic higher order components the Container approach works better.
If you e.g have 4 elements to render that could have a HOC defined, you would like to create the Higher Order Component inside render, but since calling higher order components inside render causes the <HigherOrderComponent/>'s to remount on every render this becomes a very bad Idea.
This is documented here; https://github.com/facebook/react/blob/044015760883d03f060301a15beef17909abbf71/docs/docs/higher-order-components.md#dont-use-hocs-inside-the-render-method.
But in general I would go for the HOC approach.
Related
I'm new to ReactJs and trying to follow best practices. From my research, I've come across a couple of contradicting articles discussing how implementation should be.
Should state rely on the properties being passed down from a parent component? In the comparisons below, they are both following SRP, but not sure which is best. Would like your advice, Thanks!
1. -- Best Practices for Component State in React.js
First, and probably the most important of all, the state of a component should not depend on the props passed in. (see below for example of what we should not do)
class UserWidget extends React.Component {
// ...
// BAD: set this.state.fullName with values received through props
constructor (props) {
this.state = {
fullName: `${props.firstName} ${props.lastName}`
};
}
// ...
}
2. -- 7 architectural attributes of a reliable React component
Let's refactor to have one responsibility: render form fields and attach event handlers. It shouldn't know how to use storage directly.....The component receives the stored input value from a prop initialValue, and saves the input value using a prop function saveValue(newValue). These props are provided by withPersistence() HOC using props proxy technique.
class PersistentForm extends Component {
constructor(props) {
super(props);
this.state = { inputValue: props.initialValue };
}
// ...
}
3. -- In my case, I have something like the following (wondering if this is an acceptable implementation?) - Should state be handled in Tasks, or in another TasksWithPersistence type of component that sits between TasksWithData and Tasks?
export default function TasksWithData(TasksComponent) {
return class withData extends React.Component {
render() {
const tasks = TaskAPI.getTasks();
return (
<TasksComponent
tasks={tasks}
{...this.props}
/>
)
}
}
}
export default class Tasks extends React.Component {
state = {
tasks: [],
addItemInput: null
};
// ...
componentDidMount() {
this.updateComponentState({tasks: this.props.tasks});
}
componentDidUpdate() {
this.prepUIForNextAddition();
}
// ...
}
The gist of your question seems to revolve around the anti-pattern that is to take some props and duplicate it into the state. This, mutating of props, isn't the purpose of the state. Props are immutable, duping them to the state defeats this design.
The purpose of the state is to manage things that are specific to the React Component, i.e. tightly scoped to only that React component. For instance a showHide switch for something to display within the React component. Think of the state as a locally scoped variable if it helps.
Most of the time this anti-pattern of duping the props can be satisfied by a function within the React object. For example, your state.full_name variable becomes a named function, fullName, bound to the React Component. (all code examples are assuming JSX syntax)
Note: in JavaScript camelcase is the naming structure for functions and variables, I'm assuming you're coming from ruby based on the underscore naming convention. IMO it's best to stick to the convention of the language with which you're writing the code. This is why I use camelcased naming.
...
fullName() {
return this.props.firstName + " " + this.props.lastName
}
...
That function can then be called within the render of the component
# in render() portion of your React component, assuming jsx syntax
<p>Hello, {this.fullName()}</p>
Note: Remember that in ES6 you have to bind the methods in your react class in the constructor or use => syntax so that you can call them with this.
...
constructor(props) {
super(props);
this.fullName = this.fullName.bind(this);
}
...
You could also decompose the relevant parts to a new Component called FullName if it will be utilized by multiple components.
<FullName firstName={this.props.firstName} lastName={this.props.lastName} />
Technically, "the react way" is, at least in this author's opinion, to decompose this into another component for reusability. However component reuse needs to be weighed against the complexity added, i.e. don't optimize prematurely. So you may not want to take that too far at first. The times when it's necessary will emerge naturally.
A very broad generalization of React's props is that they are guaranteed, are immutable, and they flow down like a waterfall from the topmost component. If you need to update them, update them at the highest level where it makes sense.
In a soley React based approach, if you have something that a parent needs to be aware of, "lift" that part of the code up to the parent and vice versa bind it down to the child as a props, e.g. an AJAX function that calls an API. I think of it as trying to keep the components as dumb as possible.
The parent becomes the "source of truth" for the item you "lifted". The parent handles the updates, and then passes the results to the children. So in the parent, it may exist as a state variable and then get passed as props to the child object, which then passes it along as props to it's child object, etc. The children would update as the state gets changed in their parent when it propagates down through the chain as props.
If your app is React only, i.e. no stores that manage objects such as in the flux pattern or redux pattern, you may have to store things in the topmost objet's state which technically could be viewed as bad. As your system becomes more complex, this functionality would be better handled by flux or redux's parts.
Hope this helps!
There is a huge difference between example 1 & 2.
In example #1, the reason it's bad to set state from the those props in that way is that if the props change, the widget will not update. Best practices or not, that is just wrong and bad in any framework. In that particular case, there really is no point in even using the state. Props alone will suffice.
In example #2 the prop is only being used to give the state an initial value (The prop is even named initialValue), implying that further changes to the state will be controlled by the component regardless of prop changes. It does not break single responsibility principle to use props for an initial state, especially when it's explicitly use for that purpose.
I really don't see those two examples as being contradictory because they are completely different. Further, there is no rule in single responsibility principle that you can't set state from props, you just need to pay attention to the context in which you are doing it.
One thing I had learned about React is that if the props to a component don’t change, then React doesn’t bother re-rendering the component. Is that true for stateless components too? Or do they behave more like “stupid” functions and get executed every time?
For example, if I had:
import StatelessComponent from '../StatelessComponent';
export default class DocumentsTable extends React.Component {
state = {
something: 'foobar',
};
render() {
return (
<div>
{ this.state.something }
<StatelessComponent theOnlyProp='baz'>
</div>
)
}
};
When this.state.something updates its value, does <StatelessComponent> get re-rendered? Or is it “smart” enough to see that its props didn’t change, like other React components?
UPDATE 25.10.2018
Since React 16.6, you can use React.memo for functional components to prevent re-render, similarly to PureComponent for class components:
const MyComponent = React.memo((props) => {
return (
/* markup */
);
});
Also, memo does internal optimization.
And unlike a userland memo() higher-order component implementation, the one built into React can be more efficient by avoiding an extra component layer.
Blockquote
OLD ANSWER
Yes, they always re-render 1 (unless you use React.memo as explained above) if setState() is called in the component itself or one of its parents, because functional stateless components don't carry a shouldComponentUpdate. In fact, each React component is being re-rendered1 unless they implement shouldComponentUpdate.
Important to note is that calling render() doesn't mean that DOM Nodes are being manipulated in any way. The render method just serves the diff algorithm to decide which DOM Nodes need to really be attached / detached. Note that render() is not expensive, it's the DOM manipulations that are expensive. They are executed only if render() returns different virtual trees.
From React's documentation
Just to be clear, rerender in this context means calling render for all components, it doesn’t mean React will unmount and remount them. It will only apply the differences following the rules stated in the previous sections.
Just don't worry and let render() be called unless your component is huge, then you're better off with stateful Component that implements shouldComponentUpdate().
Look here for an interesting discussion.
1 means that render() function of the component is called, not that the underlying DOM node is being manipulated.
See react does not only rerenders only If props are changed it even rerenders itself if any state change is there. In your case the component will rerender as your state is changing. The way react works is based on an algorithm named Reconciliation, what this algorithm does is that it compares your virtual DOM with real DOM and if it sees any change then it rerender your actual DOM by replacing it with your virtual DOM so any change in state will cause rerendering of the whole component.
Will a Stateless component re-render if its props have not changed?
Yes. Stateless render function will be called even if nothing has changed. However, React will in the reconciliation phase compare the virtual DOM (generated by the render function) against the existing DOM. This is far in the pipeline, hence not ideal if the render function was costly to compute.
A Pure component does have a default shallow comparison of the property and would have stopped the render to be executed. See the Pure component as a normal class React component that has a shouldComponentUpdate that compare with a triple equal the existing properties and the new one.
That being said, you can wrap your Stateless component into a Pure Component by using Recompose.pure (https://github.com/acdlite/recompose/blob/master/docs/API.md#pure) which will automatically perform, like the Pure Component, a shallow comparison without compromising on the short syntax of the Stateless component.
import StatelessComponent from '../StatelessComponent';
const PureChildFromStatelessComponent = Recompose.pure(StatelessComponent);
// ...
<PureChildFromStatelessComponent ... />
A basic question I need help here.
Whenever this.setState invoked at parent components, all the children components will be rendered. This will cause the performance issue if I have huge amount of child components.
Lets give an example,
Parent Component
handleToggleTick() {
const newObj = Object.assign({}, this.state, { iconName: ''});
this.setState({
iconName: newObj.iconName,
});
}
render() {
return(
<ChildComponentA iconName={this.state.iconName} toggleTick={() => this.handleToggleTick}></ChildComponentA>
<ChildComponentB></ChildComponentA>
<ChildComponentC></ChildComponentA>
)
}
Based on the example above, whenever handleToggleTick invoked from childcomponentA, setState invoked for new iconName. What I want is, only ChildComponentA only the one get render since props.iconName is related to it, but not for childcomponentB and childcomponentC.
I understand there is an option to check shouldComponentUpdate in childcomponent to prevent it get render. But, imagine I have over 100 of childcomponent, would it be frustrating to write over 100 times of shouldComponentUpdate method?
I need help here, please advice!
React doesn't provide any way to render children selectively. The component will either render or not. But I need to highlight a few points why this is not a problem when we use React in practice.
First of all, you don't need to manually implement shouldComponentUpdate for each component. If you don't want to rerender component if its props and state haven't changed, you can just extend from the PureComponent class instead of the Component class. Note that React.PureComponent's shouldComponentUpdate() only uses shallow comparison for state and props. But this shouldn't be a problem if you follow react best practices and avoid mutating the state.
Also, it's not practical to have more than 100 different components in one render method. React always encourages decomposing your UI into smaller components and using component composition. When we follow this approach, components will be nested inside each other in different levels instead of having a large number of components in one render method.
What I'm trying to explain is it's more practical and easy to manage when we compose our component in a nested fashion (2) rather than having lots of components inside a big container component (1).
In your example, if ChildComponentB and ChildComponentC are inside another component called ChildConatainerComponent then we only need to implement shouldComponentUpdate() for ChildConatainerComponent. Then it will automatically stop rendering any child element inside it.
render() {
return(
<ChildComponentA iconName={this.state.iconName}
toggleTick={() => this.handleToggleTick}/>
<ChildConatainerComponent/>
)
}
class ChildConatainerComponent extends PureComponent {
render() {
return (
<div>
<ChildComponentB/>
<ChildComponentC/>
</div>
);
}
}
Another very import concept to keep in mind is calling render function doesn't mean that React recreates all the DOM elements again. The render method only make changes to React virtual DOM which is an in-memory representation of DOM and it's faster than actual DOM. Then React compare versions of virtual DOM which are before the update and after the update and the actual DOM will be updated with only what has actually changed.
Another solution you could consider is moving iconName into ChildComponentA, considering this is the only component related to it.
When I develop a React-based web-app, I often separate components into smart and dumb and also into reusable and custom.
Reusable components can be self-sufficient, such as e.g. <RedButton> or <CustomSelect> but they can also be middleware components, such as <FluxStoreBinder>. A middleware component renders its children while adding some functionality to them, usually such as subscribing-reading to/from a Flux store, or wrapping into some other stateful thing. However, some extra work is needed to connect a reusable smart middleware component to a dumb component because their props won't likely match. E.g. a <FluxStoreReader> may "return" a property named data, while a child of type <ToDoList> expects toDoItems.
The question which I want to ask is how to tell a middleware component which content to render in which way. What is the proper and recommended approach? Currently I've seen 3 ways of telling a middleware component how to render its children:
By providing a function through props, such as render={({arg1}) => <Child prop1={arg1}/>}. The features are: you can access own state/props/etc within this function; you can process and re-map props; you can specify which child to render depending on a condition; you can set needed props to the child without having to proxy through the middleware component.
By returning React.cloneElement(children, props) while providing a function to remap props.
By rendering React.cloneElement(children, props) and proxying received props down to the child. Pure component approach, no callbacks. This one don't have the features/flexibility of the above 2, and also requires some extra work: you need another middleware between your middleware and its child to re-map the props.
The fourth option suggested by Mike Tronic is to use higher-order components, which are basically component factories, where one of the required arguments is a child component class. It's almost the same as #3 - but you can't even change the type of the child once you've run the factory.
Which approach did you choose for your application? Why? Please share thoughts.
Would be great to hear a React guys' opinion.
check https://www.youtube.com/watch?v=ymJOm5jY1tQ
http://rea.tech/reactjs-real-world-examples-of-higher-order-components/ and
http://www.darul.io/post/2016-01-05_react-higher-order-components
What are Higher Order Components?
A Higher Order Component is just a React Component that wraps another one.
This pattern is usually implemented as a function, which is basically a class factory (yes, a class factory!), that has the following signature in haskell inspired pseudocode
hocFactory:: W: React.Component => E: React.Component
Where W (WrappedComponent) is the React.Component being wrapped and E (Enhanced Component) is the new, HOC, React.Component being returned.
The “wraps” part of the definition is intentionally vague because it can mean one of two things:
Props Proxy: The HOC manipulates the props being passed to the WrappedComponent W,
Inheritance Inversion: The HOC extends the WrappedComponent W.
We will explore this two patterns in more detail.
What can I do with HOCs?
At a high level HOC enables you to:
Code reuse, logic and bootstrap abstraction
Render Highjacking
State abstraction and manipulation
Props manipulation
We will see this items in more detail soon but first, we are going to study the ways of implementing HOCs because the implementation allows and restricts what you can actually do with an HOC.
It's common for us to have deeply nested components with props passed from the top down via object spread:
render() {
return <MyComponent { ...this.props } />;
}
In many cases, components in the middle are not aware of the props flowing through them this way, and to annotate every prop flowing through every component would require that these compositional components know everything about every child.
Is there a way to avoid this, such that props annotated at the top of the hierarchy will be checked against their usage in the bottom of the hierarchy, without needing to annotate inside every component between, and without simply exporting and importing type aliases, which would break the hierarchical relationship?
Try using Flow's typeof operator by declaring ParentComponent.someProp to have the same type as ChildComponent.someOtherProp.