# components
elements are immutable, components may have state (when defined as classes).
component objects have attributes with special meaning, these are

-   `this.props`
-   `this.state`.

`this.props` and `this.state` may be update asynchronously, to use their values
to calculate next state use:

```js
this.setState({value: "some value"})
this.setState((state, props) => {value: state.value + 1})
```

# naming conventions
inside components handlers are prefixed w/ `handle`, like `handleChange`,
`handleSubmit`, ... handler arguments may be events (in case of native dom
components) or plain data (in case of custom components).
handlers given from outside via properties are prefixed w/ `on`, like
`onChange`, `onSubmit`, ...