What Is React?
React is a declarative, efficient, and flexible JavaScript library for building user interfaces. It lets you compose complex UIs from small and isolated pieces of code called “components”.
React in plain english
React is often described as “the V in the MVC structure”. This also happens to be the least tangible explanation one could give a newcomer, as (V)iews are typically logic-less files that are driven by a controller. Further, frameworks like Angular, Backbone, Ember, and more already have sufficient view layers — which then begs the question, why do we need to replace the V in MVC with React?
The answer is that React doesn’t necessarily want to replace our views — it wants to augment them by allowing you to create highly reusable UI components (tab bars, comment boxes, pop up modals, lists, sortable tables, etc).
In other words, the big idea behind React is this: what if you could create your own HTML element that has customized functionality? For example, one could make a <CommentBox> element that would display a textarea, run validations on the text typed into the textarea, submits the form when the enter key is pressed, etc — all just by including one line of code: <CommentBox></CommentBox>. (For those of you coming from the Angular world, you can think of React Components as a close analogy to Directives).
Declarative
React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes. Declarative views make your code more predictable and easier to debug.
Component-Based
Build encapsulated components that manage their own state, then compose them to make complex UIs. Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep state out of the DOM.
Learn Once, Write Anywhere
We don’t make assumptions about the rest of your technology Stack, so you can develop new features in React without rewriting existing code.
React can also render on the server using Node and power mobile apps using React Native.
A Simple Component
React components implement a render() method that takes input data and returns what to display. This example uses an XML-like syntax called JSX. Input data that is passed into the component can be accessed by render() via this.props.
JSX is optional and not required to use React. Try the Babel REPL to see the raw JavaScript code produced by the JSX compilation step.
class HelloMessage extends React.Component {
render() {
return (
<div>
Hello {this.props.name}
</div>
);
}
}
ReactDOM.render(
<HelloMessage name="Taylor" />,
document.getElementById('hello-example')
);