Q:

React efficient way to bind event to many dom elements

Because we add onClick handlers directly to components... eg:
<button onClick={dosomething}>Click</button>

Is there an efficient way to do this (not adding an onClick to every element) when we're dealing with dozens of elements ?
For example, in my backbone apps I would just apply a handler to a class:
events:
 'click .someclass': 'doSomething'

The backbone way seems much cleaner and easier to manage. Is there a way to emulate this behavior with React Components?
To add some perspective, I have say a dozen or more form elements that when any of them are changed, I want to potentially runs some logic. They could be text boxes, radio buttons, etc.

A:

This optimization is not needed. It would if you were coding in other libraries like jQuery, but React does this automatically for you. 
I quote:

Event delegation: React doesn't actually attach event handlers to the nodes themselves. When React starts up, it starts listening for all events at the top level using a single event listener. When a component is mounted or unmounted, the event handlers are simply added or removed from an internal mapping. When an event occurs, React knows how to dispatch it using this mapping. When there are no event handlers left in the mapping, React's event handlers are simple no-ops. To learn more about why this is fast, see David Walsh's excellent blog post.

Seen here: https://facebook.github.io/react/docs/interactivity-and-dynamic-uis.html

A:

You can apply the event handler to a common parent element instead and handle the event there:
<form onChange={this.handleChange}>
  {/* ...form elements... */}
</form>

...where the event handler determines what to do based on the event object's .target:
handleChange(e) {
  this.setState({[e.target.name]: e.target.value})
}

As a live example, I have an <AutoForm> component which uses this technique to render a <form> which handles extracting data from changed fields and the submitted form for you.

