Hello World with ReactJS – Code Example

This article represents code examples and high level concepts on React.js, a javascript library for building user interfaces, being developed by Facebook Engineers. The concepts shall be presented in detail in upcoming articles. Also, I would have to say that if you are a ReactJS expert and feel that there could be improvements with the code, please drop a line with suggestion and I shall update the article/code appropriately.

The demo of the code samples could be found on this page.

Before I go ahead and present some code samples, I have to make a mention that it was a little difficult to get started with React.js as I have been working a lot with AngularJS recently. By now, I would have to admit that they are significantly different in terms of way they help us do things with UI. I shall present another blog sighting key differences between them. However, at a high level, following are some of the reasons why I had a slightly steeper learning curve with ReactJS as well:

• Component-oriented: It is component-oriented, meaning, it requires you to think UI elements as components. Interestingly, components are composable. This means that a component can have one or more inner component. This is demonstrated in the code below.
• JSX Syntax: It uses an interesting JSX (XML-ish) syntax for writing the code. JXS transformer (a precompiler) is used to translate the syntax to the plain JavaScript.
• Event Delegation Model: It follows the event delegation model to capture events.

Following are key concepts that are demonstrated in the code.

• Components
• Event delegation
• JSX syntax

Following is brief of what is achieved along with components description

– There is an input element where users can enter their names. It is represented using “UserName” component later in the article.
– There is a div element which displays “Hello, username”. It is represented using “HelloText” component later in the article.

Following is how it is designed. Also, find the code representing the below concepts.

 //
      // This is the parent component comprising of two inner components
      // One of the component is UserName which is used to allow user to enter their name
      // Other component is HelloText which displays the text such as Hello, World
      //
      var SayHello = React.createClass({
        // This is used to set the state, "data" which is 
        // accessed later in HelloText component to display the updated state
        // 
        getInitialState: function() {
          return {data: 'World'}
        },
        // It is recommended to capture events happening with any children
        // at the parent level and set the new state that updates the children appropriately
        handleNameSubmit: function(name) {
          this.setState({data: name});
        },
        // Render method which is comprised of two components such as UserName and HelloText
        //
        render: function() {
         return(
           <div>
            <UserName onNameSubmit={this.handleNameSubmit}/>
            <HelloText data={this.state.data}/>
           </div>
           );
        }
      });

var UserName = React.createClass({
        handleChange: function() {
          var username = this.refs.username.getDOMNode().value.trim();
          this.props.onNameSubmit({username: username });
          this.refs.username.getDOMNode().value = '';
          return false;
        },
        render: function() {
         return(
          <form role="form" onChange={this.handleChange}>
             <div className="input-group input-group-lg">
                <input type="text" className="form-control col-md-8"  placeholder="Type Your Name" ref="username"/>
             </div>
          </form>
          );
        }
      });

var HelloText = React.createClass({
          render: function() {
            return (
            <div>
              <h3>Hello, {this.props.data}</h3>
            </div>
            );
          }
      });

If you would like to get a quick hold on entire code, I have put it up on this github hello-reactjs page. Feel free to comment/suggest.

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• Author
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Ajitesh Kumar

I have been recently working in the area of Data analytics including Data Science and Machine Learning / Deep Learning. I am also passionate about different technologies including programming languages such as Java/JEE, Javascript, Python, R, Julia, etc, and technologies such as Blockchain, mobile computing, cloud-native technologies, application security, cloud computing platforms, big data, etc. I would love to connect with you on Linkedin.
Check out my latest book titled as First Principles Thinking: Building winning products using first principles thinking.

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