Detailed explanation of functional subcomponents and higher-order components in React

This article brings you a detailed explanation of function subcomponents and high-order components in React. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

After coming into contact with React projects, most people should have already understood or used HOC (High-Order-Components) and FaCC (Functions as Child Components), because these two patterns are widely used It exists in most react open source libraries. For example, withRouter in react-router is a typical high-order component, which accepts one component and returns another enhanced component. Motion in react-motion is a typical FaCC application.

HOC and FaCC do very similar things, both are similar to the decorator pattern in the design pattern. All functions are enhanced on the original instances or units.

Of course, it is not only used in some open source libraries, but also in daily code writing, there are many places where it is suitable to use HOC and FaCC to encapsulate some logic. For example, data burying points, toggle of new features, obtaining conversion data, etc. Very useful for enhancing code readability and logic reuse.

HOC

We have all used high-order functions, which accept a function and return an encapsulated function:

const plus = first => second => (first + second)
plus(1)(2) // 3

And high-order components are the concept of high-order functions. Applied to higher-order components:

const withClassName = ComposedComponent => props => (
   <ComposedComponent {...props} className=&#39;demo-class&#39; />
)

// 使用
const Header = text => (<header>{text}</header>)
const headerWitheClass = withClassName(Header)

Accepts a component and returns a wrapped new component. The withRouter we often use is to add properties such as localtion to the original component props. In addition to adding props, high-order components can also do:

• Do some things before and after actually calling the component, such as burying data, etc.

• Determine whether the component should be rendered, or should render other things, such as rendering the error page after an error

• Pass props and add new props

• Instead of rendering the component, do some other things, such as rendering an external dom

The first three points above are relatively easy to understand. Please explain the fourth point. For example, after rendering a page, you need to change the title of the page. This is a common requirement for single-page applications. Usually you can use hooks in a specific router library to achieve this. Of course, it can also be achieved through HOC:

const withTitleChange = ComposedComponent => {
  return class extends React.Component {
    componentDidMount () {
      const { title } = this.props
      document.title = title
    }
    render () {
      const props = this.props
      return <ComposedComponent {...props} />
    }
  }
}

FaCC

Similarly, FaCC is also a mode used to enhance the capabilities of original components. Its main function is realized by react's props.children can be Anything, including functions. We can take the above class example and implement it again with FaCC:

const ClassNameWrapper = ({ children }) => children('demo-class')

// 使用

const HeadWithClass = (props) => (
  <ClassNameWrapper>
    {(class) => <header classNmae={class} ></header>}
  </ClassNameWrapper>
)

In FaCC, you can also do many things in the life cycle like HOC to encapsulate the original components. Basically, HOC can do FaCC can do it too. The project I was working on used to use HOC on a large scale. After some discussions, it began to transform into FaCC on a large scale.

Difference

Both are used to enhance the original components. Which one should be used? Which is the correct model? There are a lot of discussions about this in the community. For example, some people say that FaCC is an anti-pattern: Function as Child Components Are an Anti-Pattern. The reason he gave is that children are not semantic and will cause confusion. Then he proposed the Component Injection model, which interested students can read.

Let’s make a comparison from several aspects:

1. combination stage

The combination stage means HOC, FaCC and When combining enhanced components. It can be clearly found that FaCC displays more dependency information on the docking of front and rear components, which is relatively easier to understand. As for HOC, how to bridge each other, you have to go deep into the HOC and read the code to know what this HOC does.

// HOC example
import View from './View'

const DetailPage = withServerData(withNavigator(View))

// FaCC example

import View from './View'

const DetailPage = props => (
  <FetchServerData>
    {
      data => (
        <Navigator>
          <View data={data} {...props} />
        </Navigator>
      )
    }
  </FetchServerData>
)

If you add 2 more HOCs on top, the above combination process will become very ugly. Relatively speaking, with FaCC, how it is encapsulated, where the data source comes from, and what data the component receives are all more conspicuous.

1. Performance Optimization

In HOC we can receive props from the host, because props are passed down from HOC, so we also have For the complete life cycle, we can use shouldComponentUpdate optimization. This is not the case with FaCC. Props cannot be compared internally. Props cannot be compared unless an external component is packaged during combination.

1. Flexibility

FaCC is more flexible than HOC in the combination phase. It does not stipulate how the enhanced component uses the attributes it passes. . The HOC is basically finalized after it is written.

In addition, FaCC will not create a new Component, while HOC will create a new Component and pass props to it.

Summary

Many open source libraries in the community have used the two modes, and there are many articles comparing them. There was also a lot of heated discussion, and of course both models were good for finally solving the problem. Due to different considerations, the choice may be different.

Related recommendations:

React high-order component instance analysis

Instances of controlled components and uncontrolled components in React Detailed explanation

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