This article represents Hello World example in ReactJS with explanation on how one could think in component-oriented manner when working with ReactJS. Please feel free to comment/suggest if I missed to mention one or more important points. Also, sorry for the typos.

• Hello World Code Sample
• Thinking & Programming Hello World
###### Hello World Code Sample

Paste the code below in an HTML file and open up in a browser. The text, “Hello, Calvin” will get printed.

<!DOCTYPE html>
<html>
<title>Hello ReactJS!</title>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.13.3/react.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/0.13.3/JSXTransformer.js"></script>
<body>
<div id="content"></div>
<script type="text/jsx">
var HelloMessage = React.createClass({
render: function() {
return (
<h1>Hello, {this.props.name}</h1>
);
}
});
React.render(<HelloMessage name="Calvin"/>, document.getElementById("content"))
</script>
</body>
</html>

###### Thinking & Programming Hello World

In above example, pay attention to some of the following:

• There is div with id as “content”. React will rendor the “Hello, Calvin” within this div element. The code related with this is following:
React.render(<HelloMessage name="Calvin"/>, document.getElementById("content"))


When working with ReactJS programming, one would want to break page as several components, one containing others, and render the top-level component using the above code. I would illustrate this concept with an example in another article on how to think and program “Hello, Calvin” with a text box entry.

• React.render would take the component along with one or more properties/attributes which could be used to pass the input to the component. In above example, React takes input as HelloMessage component and pass the name “Calvin” as property through property, “name”.
• Once that is done, its time to define HelloMessage component. Following minimal template code is used to define a component:
var ClassName = React.createClass({
render: function(){
return(
//To be rendered element/component goes here
);
}
});

• Using above code, one would define HelloMessage component as following. This component returns div element in which the property name is referenced using {this.props.name}
var HelloMessage = React.createClass({
render: function() {
return (
<h1>Hello, {this.props.name}</h1>
);
}
});

• One must note that all of the above code needs to be defined under following:
<script type="text/jsx">
</script>

That is it. To summarize, keep following in mind:

• Break the page in components with one component containing other components.
• Use React.render() method to render the top level component.

Hope you found it useful. Please feel free to share/comment.