React uses a declarative paradigm that makes it easier to reason about your application.
React computes the minimal set of changes necessary to keep your DOM up-to-date.
React works with the libraries and frameworks that you already know.
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.
In addition to taking input data (accessed via `this.props`), a
component can maintain internal state data (accessed via `this.state`).
When a component's state data changes, the rendered markup will be
updated by re-invoking `render()`.
This example demonstrates use of React without JSX.
Using `props` and `state`, we can put together a small Todo application. This example uses `state` to track the current list of items as well as the text that the user has entered. Although event handlers appear to be rendered inline, they will be collected and implemented using event delegation.
React is flexible and provides hooks that allow you to interface with other libraries and frameworks. This example uses Showdown, an external Markdown library, to convert the textarea's value in real-time.