Q:

Why React component is launching onClick event on render, but not when clicked?

I have a React component like this:
import React, { Component, PropTypes } from 'react';
import SubnavActions from '../../actions/subnav-actions';
import FeedActions from '../../actions/feed-actions';

export default class SubnavItemModule extends Component {

  render() {

    return (

      <div className={'item ' + this.props.active} thumbImg={this.props.thumbImg} _text={this.props._text} _id={this.props._id} onClick={this.handler}>
        <p>{this.props._text}</p>
      </div>
    );
  }

  handler() {

    console.log('subnav-filter-item-module handler launching');
  }
};

onClick{this.handler} used to work before, but now it launches onClick event everytime the component is rendered.
If I click it though, nothing happens.
In other demo I used onClick={ e => this.handler(e)} succesfully, but in this work nothing happens.
I started using Babel 6 and Babelify before this occured, but I can't really understand here what is causing and what. Earlier I used Reactify. So my questions are the following:

What is the proper way to launch the onClick event here?
Why is it launched on render?
Is this related to Babelify/Reactify? If so, how?

EDITS:
Corrected the original code sample.
Here is the parent module:
http://pastebin.com/rSKf4wR8
If you wonder why am I writing that differently (using import instead of require), I am in the middle of changing the syntax. If you ask why, well, I don't know. I just try to follow some tutorials and see how others write. I don't really even know the difference between require and import.
Also, I just realised something. Can this be caused because I am not passing any function as a prop in the parent?
Somebody is having similar issue with Rails app, does this provide any more info: React rails app not executing onClick handler when props are used in a conditional expression

A:

In your case you call function, but you need pass to onClick reference to function
onClick={ this.handler }

Example
if you need pass some argument to handler you can use .bind, like this
onClick={ this.handler.bind(this, 100) }

handler(x) {}

Example
or with arrow function 
onClick={ () => this.handler(100) }

