For a simple component written like this:
import React from 'react'
const MyComponent = ({text}) => {
return(<div> {text} </div>
}
Is there a syntax for implementing lifecycle method like componentDidMount() or do I have to convert code to React.Component class?
Is there a syntax for implementing lifecycle method like componentDidMount()
No.
do I have to convert code to React.Component class?
Yes.
See https://facebook.github.io/react/docs/state-and-lifecycle.html
In the alpha version of React there is an opt in feature called hooks which will address this. See more on hooks here https://reactjs.org/docs/hooks-overview.html
Related
I wrote a component Foo in React.js (its parameter "interface" consists of a single parameter text; there are more parameters in my real code):
import React from 'react';
export default class Foo extends React.Component {
constructor(props){
super(props);
}
render(){
return <div>{this.props.text}</div>;
}
}
and I thought I could improve the code by modifying the property access as:
import React from 'react';
export default class Foo extends React.Component {
constructor(props){
super(props)
this._text = props.text
}
render(){
return <div>{this._text}</div>;
}
}
This would give me the benefits that
I can immediately see what properties are supported by having a look at the constructor.
The code that applies the properties gets shorter/better to read.
However, this destroys the update workflow for the property. In a parent component I use Foo like
<Foo text={this.state.parentText}/>
and
this.setState({parentText: "new text"})
does not trigger an update of the text in Foo any more. The constructor of Foo is only called once and therefore, the private variable this._text is not updated on property changes.
=> Using extra private properties to modify the parameter access turned out to be a bad idea.
=> What would you recommend to have a clear interface for the component without breaking the update workflow?
Some ideas:
a) List all used properties at the start of render (and componentDidUpdate)
render(){
const text = this.props.text;
return <div>{text}</div>;
}
b) Create a getter for each property and put them directly under the constructor, for example
get _text(){
return this.props.text;
}
c) (Only for shorter access.) Try to avoid class components. With function components there is direct access with props.text instead of this.props.text. Or, as a workaround, inherit from a custom component class that passes props argument to render:
render_props(props){
...
}
(Why doesn't react pass this.props as an argument to render by default?)
d) Document the supported properties in a doc string
=> If you know a better option / some standard / best practice, please let me know.
Also tried but failed:
I tried to use state in the child component, with the hope that it would be automatically updated on updates of the parent state:
import React from 'react';
export default class Foo extends React.Component {
constructor(props){
super(props)
this.state = {
text: props.text
}
}
render(){
return <div>{this.state.text}</div>;
}
}
However, this also breaks the update workflow. Using this.state only seems to make sense in the parent component.
Related:
Can I update a component's props in React.js?
https://github.com/vasanthk/react-bits/blob/master/anti-patterns/01.props-in-initial-state.md
Related topic:
How to interact with third party libraries using function components?
https://reactjs.org/docs/integrating-with-other-libraries.html
How do I use/include third party libraries in react?
Integrating React with Other Libraries
Use function components for React >= 16.8, also see recommendation at
https://www.w3schools.com/react/react_class.asp
Use useState hooks instead of setState. This is the modern way to write React, and gives you a simpler way to access state (foo.text, foo.setText). https://reactjs.org/docs/hooks-state.html
Typescript would help with docs (type props = { text: string }), but I also would like the answer for d) (your question is several questions I think).
Use props.text directly, instead of using extra shortcut variable const text = props.text suggested by option a). This way, you don't have a list of all available properties on top of the component function. However, using a consistent props. prefix makes it easier to spot the injected variables in the react code. If there is a huge number of properties and its hard to identify them, try to improve modularization.
JavaScript example code:
Child component Foo:
import React from 'react';
export default function Foo(props){
return <div>{props.text}</div>;
}
}
Parent component:
import React, { useState } from 'react';
import Froo from './foo';
export default function Parent(){
const [parentText, setParentText] = useState('Hello world');
return <Foo text={parentText}/>;
}
In my mental model, React function components are basically class components stripped down to render method (and this is reinforced by React docs saying that that render should be a pure function of state and props). I assume that render method and Functional components are called at the same phase of React lifecycle so why I can't use hooks in render method? To be more precise, I want to know the technical limitations of class components which disallow hooks usage.
import React from "react";
export default class App extends React.Component {
render() {
const [state, setState] = React.useState(0); // Invalid hook call. Hooks can only be called inside of the body of a function component.
return (
<div>
<h1>Hello World</h1>
</div>
);
}
}
no, we can't use hooks with class component. So, please, read the documentation
Rules of hooks:
✅ Call Hooks from React function components.
✅ Call Hooks from custom Hooks (we’ll learn about them on the next page).
This question already has answers here:
React functional components vs classical components
(4 answers)
Closed 4 years ago.
I cannot find the source but there was a clear notice in react documentation that says arrow function, class declaration and object literals are the same as far as react is concerned. I feel that there are still certain nuances. Which format should be used in what situation? Thanks.
CompA = ()=> {}
class CompB extends React.Component {}
const CompC= () => {}
(please allow me to read/reply to answers/comment in a few hours. )
CompA = ()=> {} is a stateless component. It has no state and has no state and has no events like componentWillMount. It's simpler to write and read. Also, it should be faster, but it the old versions of React he has the same performance. Not sure about new versions, because in v16 React core was reimplemented.
class CompB extends React.Component {} it is a class component, you should use it when you have a component state or want to handle it lifecycle
Also, there is a class CompB extends React.PureComponent {} it's the same as Component but updates only if the state or props changes. It's really faster if you have no props with complex objects because it compares props and state before render.
Please take a look at this answers too
React functional components vs classical components
CompA = ()=> {} and const CompC= () => {} these are both same and are called functional components or stateless components.
class CompB extends React.Component {} this type is called class component or stateful components all you can access to reacts lifecycle's method in these.
Functional components are just JavaScript functions. They take in an optional input which we call props.
When you don't want to do use state and just want to display data, then you can use functional components.
The primary reason to choose class components over functional components is that they can have state.
How to signal to React that a functional component is "pure", as an equivalent of React.PureComponent for component classes?
function C(props) {
return <var>{props.n}</var>
}
without making it a class
class C extends React.PureComponent {
render() {
return <var>{this.props.n}</var>
}
}
As of React 16.6.0, memo has been added, so the answer is now:
const C = React.memo(props => {
return <var>{props.n}</var>
})
Based on the concept of purity in functional programming paradigms, a function is pure if:
Its return value is only determined by its input values
Its return value is always the same for the same input values
There seem two ways to do it for React functional components:
Using memo from react:
import React, { memo } from 'react';
const Component = (props) {
return (
// Component code
)
}
// Wrap component using "memo" HOC
export default memo(Component);
Using pure from recompose:
import React from 'react';
import { pure } from 'recompose';
const Component = (props) {
return (
// Component code
)
}
// Wrap component using "pure" HOC
export default pure(Component);
To #Shubham and #Andrew:
No, functional components are not PureComponents. Functional components will always get re-render if the parent component re-renders. A PureComponent contains a default shouldComponentUpdate() and I think that's what OP wants.
You can use pure provided by recompose to wrap and optimize your functional components:
import pure from 'recompose/pure'
const YourFunctionalComponent = (props) => {
...
}
export default pure(YourFunctionalComponent)
In addition to CodinCat answer.
The author of the library, recomponse, wrote a note on 25th Oct of 2018, where he stated, that what he tried to solve by the library was solved by the React Team through introducing hooks. Not only that, React team added optimization feature like React.memo(), which was named as React.pure() earlier. So, it's time to use React.memo(). Read Official Docs about it
I am using a component:- https://github.com/christianalfoni/formsy-react, for creating forms. I am trying to create one of my own components of the input. So as mentioned I need to use it for my's mixin. But unfortunately, there is no support for it in es6 style. So any work around anyone knows of.
here is my component code:-
import Formsy from 'formsy-react';
class DropDownAutoComplete extends React.Component {
constructor(props, context) {
super(props, context);
this.mixins = [Formsy.Mixin];
}
changeValue(event) {
this.mixins[0].setValue(event.currentTarget.value);
}
handleValue1Change(value) {
this.setState({value: value});
}
render() {
const className = this.mixins[0].showRequired() ? 'required' : this.mixins[0].showError() ? 'error' : null;
// An error message is returned ONLY if the component is invalid
// or the server has returned an error message
const errorMessage = this.mixins[0].getErrorMessage();
return <DropdownList
data={this.props.dropDownConfigs.value}
onChange={this.changeValue.bind(this)}
textField={this.props.dropDownConfigs.name}
caseSensitive={false}
filter='contains'>
</DropdownList>
}
}
It's throwing an error where the show required function is called. Apparently, its implementation uses some state variables like required.
By design, mixins do not work with ES6 classes - trying to hack something together is just going to cause you headaches!
One solution is to use what's called a higher-order component - a function that takes in a component, and returns a new component that wraps around it. These wrapper components can have lifecycle hooks of their own, and can pass props down to the wrapped components, effectively providing you with the same functionality mixins would give you, but arguably in a cleaner way!
formsy-react allows you to take this approach, providing its own HOC:
import {HOC} from 'formsy-react';
class MyInput extends React.Component {
render() {
return (
<div>
<input value={this.props.getValue()} onChange={(e) => this.props.setValue(e.target.value)}/>
</div>
);
}
};
export default HOC(MyInput);
You can use react-mixin-decorator.
Quoting from README:
If you're creating React components using ES6 classes and you'd like
to use existing mixins to add some nice functionality to your
component, you probably don't want to take the time to convert the
mixins to something that your ES6 React component class could use.