ReactJS JSX Use Shorthand to Perform Multiple Executions

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How do you render multiple child components depending on a certain condition? The answer is by using fragments.,That said, when it comes to rendering multiple elements with fragments depending on a condition, you can use any of the techniques described in this article.,In React, conditional rendering refers to the process of delivering elements and components based on certain conditions.

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And interact with the application in your browser:,Then, run the application from your terminal window:,This is the process of creating an extracted function. This code extracts the logic from JSX into a function renderAuthButton. And the function is executed within the JSX curly braces.

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Take a look at the below code:,Now, take a look at the below code:,So React, will convert this JSX to the below code:

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JavaScript does not support multiple return values., A Deeper Dive into Return Statements, JavaScript and JSX ,When you return parallel JSX elements from a Component’s render function in React, the code gets transpiled into a function that returns multiple values which is not supported in JavaScript.

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Let's create a simple Avatar component which shows a Facebook page picture and name using the Facebook Graph API.,So far, we've looked at how to write a single component to display data and handle user input. Next let's examine one of React's finest features: composability.,When you create a React component instance, you can include additional React components or JavaScript expressions between the opening and closing tags like this:

var Avatar = React.createClass({
  render: function() {
    return (
      <div>
        <PagePic pagename={this.props.pagename} />
        <PageLink pagename={this.props.pagename} />
      </div>
    );
  }
});

var PagePic = React.createClass({
  render: function() {
    return (
      <img src={'https://graph.facebook.com/' + this.props.pagename + '/picture'} />
    );
  }
});

var PageLink = React.createClass({
  render: function() {
    return (
      <a href={'https://www.facebook.com/' + this.props.pagename}>
        {this.props.pagename}
      </a>
    );
  }
});

ReactDOM.render(
  <Avatar pagename="Engineering" />,
  document.getElementById('example')
);
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I understand that arrow functions make things more efficient by not recreating the functions each render similar to how binding in the constructor works.,I understand that arrow functions make things more efficient by not recreating the functions each time they are referred to,I am using ReactJS with Babel and Webpack and using ES6 as well as the proposed class fields for arrow functions. I understand that arrow functions make things more efficient by not recreating the functions each render similar to how binding in the constructor works. However, I am not 100% sure if I am using them correctly. The following is a simplified section of my code in three different files.

This is not true. It depends on where exactly are you using the Arrow function. If Arrow function are used in render method, then they create a new instance everytime render is called just like how bind would work. Consider this example

<div onClick={()=>{this.onClick()}}>Previous</div>

However consider the case below

onClick = () => {
   console.log("Div is clicked")
}

In your case, you have used Arrow function to define prevItem and hence it gets the context of the enclosing React component.

prevItem = () => {
    console.log("Div is clicked")
}

render(){
    return (
         <SecondClass prevItem={this.prevItem} />
    )
}

Now in its child, even if you call prevItem with any custom context, using bind or arrow function, prevItem when executed in parent i.e Main.js will get the context of its enclosing React component. And since you just wish to execute prevItem function and do not want to pass any data to this from the child, writing

<ThirdClass type="prev" onClick={()=>this.props.prevItem()} />

and

<div onClick={()=>{this.props.onClick()}}>Previous</div>

is simply useless and will only add to performance implication since new functions are created in SecondClass and ThirdClass everytime. You simply don't need to have these functions defined as arrow function and could just write

<ThirdClass type="prev" onClick={this.props.prevItem} />

and

<div onClick={this.props.onClick}>Previous</div>
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The componentWillMount() is good for handling component configurations and performing synchronous calculation based on props since props and state are defined during this lifecycle method.,For handling changes to state or props in React components, we can consider the following immutable approaches:,Your application always begins with a few components. You start adding new features and dependencies, and before you know it, you end up with a huge production file.

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DOM event handlers: DOM event handlers often make a call to setState or invoke some effect in the React application such as sending data to an API server.,Render prop: A component prop that expects a function as a value. This function must return a JSX element, hence the name. Render prop is a good candidate for inline functions.,Concerns around render props: A render prop is a method that returns a React element and is used to share state among React components.

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Class components extend from React.Component.,Class-based Components uses ES6 class syntax. It can make use of the lifecycle methods.,21.What are the lifecycle methods of ReactJS?

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• React Scripts, a package that contains scripts and configurations that fulfill the requirements for React build workflow and includes development server and latest JavaScript features.,• React DOM, which it provides methods that are specific to DOM. Only the render method will be used from this module in index.js file for the purpose of rendering the application to the DOM.,The purpose of the above code is to write test for various components of the app.

1import React from "react";
2import logo from "./logo.svg";
3import "./App.css";
4function App() {
5  return (
6    <div className="App">
7      <header className="App-header">
8        <img src={logo} className="App-logo" alt="logo" />
9        <p>
10          Edit <code>src/App.js</code> and save to reload.
11        </p>
12        <a
13          className="App-link"
14          href="https://reactjs.org"
15          target="_blank"
16          rel="noreferrer noopener"
17        >
18          Learn React
19        </a>
20      </header>
21    </div>
22  );
23);
24export default App;
25// Error 
2623:1 error Parsing error: Unexpected token 21 | </div> 22 | ); > 23 | ); | ^ 24 | export default App;
27// Error
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