About React component project practice-JS Tutorial-php.cn

Before you start:

We use ES6 and ES7 syntax. If you are not very clear about the difference between display components and container components, it is recommended that you start by reading this article. If you have any suggestions or questions, please leave them in Leave a comment about class-based components in the comments.

Nowadays, React components are generally developed using class-based components. Now let’s write our component in the same line:

import React, { Component } from &#39;react&#39;;
import { observer } from &#39;mobx-react&#39;;

import ExpandableForm from &#39;./ExpandableForm&#39;;
import &#39;./styles/ProfileContainer.css&#39;;

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I like css in javascript very much. However, this method of writing styles is still too new. So we introduce css files in each component. Moreover, locally introduced imports and global imports will be separated by a blank line.

Initializing State

import React, { Component } from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;

import ExpandableForm from &#39;./ExpandableForm&#39;
import &#39;./styles/ProfileContainer.css&#39;

export default class ProfileContainer extends Component {
 state = { expanded: false }

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You can use the old method to initialize state in constructor. More related information can be found here. But we choose a clearer approach.

Also, we make sure to add export default in front of the class. (Translator's note: Although this may not be correct when using redux).

propTypes and defaultProps

import React, { Component } from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { string, object } from &#39;prop-types&#39;

import ExpandableForm from &#39;./ExpandableForm&#39;
import &#39;./styles/ProfileContainer.css&#39;

export default class ProfileContainer extends Component {
 state = { expanded: false }
 
 static propTypes = {
  model: object.isRequired,
  title: string
 }
 
 static defaultProps = {
  model: {
   id: 0
  },
  title: &#39;Your Name&#39;
 }

 // ...
}

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propTypes and defaultProps are static properties. Define it as early as possible in the component class so that other developers can notice it immediately when reading the code. They can serve as documentation.

If you use React 15.3.0 or higher, you need to introduce the prop-types package instead of using React.PropTypes. More content moves here.

All your components should have prop types.

Method

import React, { Component } from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { string, object } from &#39;prop-types&#39;

import ExpandableForm from &#39;./ExpandableForm&#39;
import &#39;./styles/ProfileContainer.css&#39;

export default class ProfileContainer extends Component {
 state = { expanded: false }
 
 static propTypes = {
  model: object.isRequired,
  title: string
 }
 
 static defaultProps = {
  model: {
   id: 0
  },
  title: &#39;Your Name&#39;
 }
 handleSubmit = (e) => {
  e.preventDefault()
  this.props.model.save()
 }
 
 handleNameChange = (e) => {
  this.props.model.changeName(e.target.value)
 }
 
 handleExpand = (e) => {
  e.preventDefault()
  this.setState({ expanded: !this.state.expanded })
 }

 // ...

}

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In class components, when you pass methods to child components, you need to ensure that they are used correctly when called. of this. This is usually done when passing it to a child component: this.handleSubmit.bind(this).

It’s much simpler to use the ES6 arrow method. It automatically maintains the correct context (this).

Pass a method to setState

In the above example, there is this line:

this.setState({ expanded: !this.state.expanded });

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setState It’s actually asynchronous! In order to improve performance, React will call setState that is called multiple times together. Therefore, the state may not necessarily change immediately after calling setState.

So, when calling setState, you cannot rely on the current state value. Because i doesn't know its value at all.

Solution: Pass a method to setState, and pass the state value before the call as a parameter to this method. Take a look at the example:

this.setState(prevState => ({ expanded: !prevState.expanded }))

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Thanks to Austin Wood for the help.

Disassemble the component

import React, { Component } from 'react'
import { observer } from 'mobx-react'

import { string, object } from 'prop-types'
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'

export default class ProfileContainer extends Component {
 state = { expanded: false }
 
 static propTypes = {
  model: object.isRequired,
  title: string
 }
 
 static defaultProps = {
  model: {
   id: 0
  },
  title: 'Your Name'
 }

 handleSubmit = (e) => {
  e.preventDefault()
  this.props.model.save()
 }
 
 handleNameChange = (e) => {
  this.props.model.changeName(e.target.value)
 }
 
 handleExpand = (e) => {
  e.preventDefault()
  this.setState(prevState => ({ expanded: !prevState.expanded }))
 }
 
 render() {
  const {
   model,
   title
  } = this.props
  return ( 
   
    
     
{title}
     
    
   
  )
 }
}

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If there are multiple lines of props, each prop should be single Own a line. Just like the above example. The best way to achieve this goal is to use a set of tools: Prettier.

Decorator

@observer
export default class ProfileContainer extends Component {

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If you know some libraries, such as mobx, you You can use the above example to modify class components. A decorator is a method that passes a class component as a parameter.

Decorators can write more flexible and readable components. If you don’t want to use a decorator, you can do this:

class ProfileContainer extends Component {
 // Component code
}
export default observer(ProfileContainer)

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Closure

Try to avoid it in child components Pass in the closure, such as:

<input
 type="text"
 value={model.name}
 // onChange={(e) => { model.name = e.target.value }}
 // ^ Not this. Use the below:
 onChange={this.handleChange}
 placeholder="Your Name"/>

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Note: If input is a React component, this will automatically trigger its redrawing, regardless of other Whether props have changed.

Consistency checking is the most resource-consuming part of React. Don't add extra work here. The best way to handle the problem in the above example is to pass in a class method, which will be more readable and easier to debug. For example:

import React, { Component } from 'react'
import { observer } from 'mobx-react'
import { string, object } from 'prop-types'
// Separate local imports from dependencies
import ExpandableForm from './ExpandableForm'
import './styles/ProfileContainer.css'

// Use decorators if needed
@observer
export default class ProfileContainer extends Component {
 state = { expanded: false }
 // Initialize state here (ES7) or in a constructor method (ES6)
 
 // Declare propTypes as static properties as early as possible
 static propTypes = {
  model: object.isRequired,
  title: string
 }

 // Default props below propTypes
 static defaultProps = {
  model: {
   id: 0
  },
  title: 'Your Name'
 }

 // Use fat arrow functions for methods to preserve context (this will thus be the component instance)
 handleSubmit = (e) => {
  e.preventDefault()
  this.props.model.save()
 }
 
 handleNameChange = (e) => {
  this.props.model.name = e.target.value
 }
 
 handleExpand = (e) => {
  e.preventDefault()
  this.setState(prevState => ({ expanded: !prevState.expanded }))
 }
 
 render() {
  // Destructure props for readability
  const {
   model,
   title
  } = this.props
  return ( 
   
    // Newline props if there are more than two
    
     
{title}
      { model.name = e.target.value }}
      // Avoid creating new closures in the render method- use methods like below
      onChange={this.handleNameChange}
      placeholder="Your Name"/>
    
   
  )
 }
}

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Method component

This type of component has no state, no props, and no methods. They are pure components that contain minimal changes. Use them often.

propTypes

import React from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { func, bool } from &#39;prop-types&#39;
import &#39;./styles/Form.css&#39;
ExpandableForm.propTypes = {
 onSubmit: func.isRequired,
 expanded: bool
}
// Component declaration

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We define propTypes before the declaration of the component.

Decompose Props and defaultProps

import React from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { func, bool } from &#39;prop-types&#39;
import &#39;./styles/Form.css&#39;

ExpandableForm.propTypes = {
 onSubmit: func.isRequired,
 expanded: bool,
 onExpand: func.isRequired
}

function ExpandableForm(props) {
 const formStyle = props.expanded ? {height: &#39;auto&#39;} : {height: 0}
 return (
  <form style={formStyle} onSubmit={props.onSubmit}>
   {props.children}
   <button onClick={props.onExpand}>Expand</button>
  </form>
 )
}

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Our component is a method. Its parameters are props. We can extend this component like this:

import React from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { func, bool } from &#39;prop-types&#39;
import &#39;./styles/Form.css&#39;

ExpandableForm.propTypes = {
 onSubmit: func.isRequired,
 expanded: bool,
 onExpand: func.isRequired
}

function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
 const formStyle = expanded ? {height: &#39;auto&#39;} : {height: 0}
 return (
  <form style={formStyle} onSubmit={onSubmit}>
   {children}
   <button onClick={onExpand}>Expand</button>
  </form>
 )
}

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Now we can also use default parameters to play the role of default props, which has good readability. If expanded is not defined, then we set it to false.

However, try to avoid using the following examples:

const ExpandableForm = ({ onExpand, expanded, children }) => {

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Looks modern, but the method is unnamed.

如果你的Babel配置正确，未命名的方法并不会是什么大问题。但是，如果Babel有问题的话，那么这个组件里的任何错误都显示为发生在 <>里的，这调试起来就非常麻烦了。

匿名方法也会引起Jest其他的问题。由于会引起各种难以理解的问题，而且也没有什么实际的好处。我们推荐使用function，少使用const。

装饰方法组件

由于方法组件没法使用装饰器，只能把它作为参数传入别的方法里。

import React from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { func, bool } from &#39;prop-types&#39;
import &#39;./styles/Form.css&#39;

ExpandableForm.propTypes = {
 onSubmit: func.isRequired,
 expanded: bool,
 onExpand: func.isRequired
}

function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
 const formStyle = expanded ? {height: &#39;auto&#39;} : {height: 0}
 return (
  <form style={formStyle} onSubmit={onSubmit}>
   {children}
   <button onClick={onExpand}>Expand</button>
  </form>
 )
}
export default observer(ExpandableForm)

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只能这样处理：export default observer(ExpandableForm)。

这就是组件的全部代码：

import React from &#39;react&#39;
import { observer } from &#39;mobx-react&#39;
import { func, bool } from &#39;prop-types&#39;
// Separate local imports from dependencies
import &#39;./styles/Form.css&#39;

// Declare propTypes here, before the component (taking advantage of JS function hoisting)
// You want these to be as visible as possible
ExpandableForm.propTypes = {
 onSubmit: func.isRequired,
 expanded: bool,
 onExpand: func.isRequired
}

// Destructure props like so, and use default arguments as a way of setting defaultProps
function ExpandableForm({ onExpand, expanded = false, children, onSubmit }) {
 const formStyle = expanded ? { height: &#39;auto&#39; } : { height: 0 }
 return (
  <form style={formStyle} onSubmit={onSubmit}>
   {children}
   <button onClick={onExpand}>Expand</button>
  </form>
 )
}

// Wrap the component instead of decorating it
export default observer(ExpandableForm)

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条件判断

某些情况下，你会做很多的条件判断：

<p id="lb-footer">
 {props.downloadMode && currentImage && !currentImage.video && currentImage.blogText
 ? !currentImage.submitted && !currentImage.posted
 ? <p>Please contact us for content usage</p>
  : currentImage && currentImage.selected
   ? <button onClick={props.onSelectImage} className="btn btn-selected">Deselect</button>
   : currentImage && currentImage.submitted
    ? <button className="btn btn-submitted" disabled>Submitted</button>
    : currentImage && currentImage.posted
     ? <button className="btn btn-posted" disabled>Posted</button>
     : <button onClick={props.onSelectImage} className="btn btn-unselected">Select post</button>
 }
</p>

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这么多层的条件判断可不是什么好现象。

有第三方库JSX-Control Statements可以解决这个问题。但是与其增加一个依赖，还不如这样来解决：

<p id="lb-footer">
 {
  (() => {
   if(downloadMode && !videoSrc) {
    if(isApproved && isPosted) {
     return <p>Right click image and select "Save Image As.." to download</p>
    } else {
     return <p>Please contact us for content usage</p>
    }
   }

   // ...
  })()
 }
</p>

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使用大括号包起来的IIFE，然后把你的if表达式都放进去。返回你要返回的组件。